RaspberryPi profile uses GCC 9 now

[uilianries]

The Base docker image is Ubuntu Focal (20.04) which recently updated the package g++-arm-linux-gnueabihf to version 9.

https://packages.ubuntu.com/focal/devel/g++-arm-linux-gnueabihf

fixes #104

Some logs:

 % docker build --platform=linux/amd64 --tag=uilianries/gcc9-armv7 --build-arg CONAN_VERSION=1.53.0 conan-training
[+] Building 84.6s (10/10) FINISHED                                                                                                                                                                                                                                             
 => [internal] load build definition from Dockerfile                                                                                                                                                                                                                       0.0s
 => => transferring dockerfile: 37B                                                                                                                                                                                                                                        0.0s
 => [internal] load .dockerignore                                                                                                                                                                                                                                          0.0s
 => => transferring context: 2B                                                                                                                                                                                                                                            0.0s
 => [internal] load metadata for docker.io/conanio/gcc10:1.53.0                                                                                                                                                                                                            2.7s
 => [1/6] FROM docker.io/conanio/gcc10:1.53.0@sha256:e38fd0ca6404b8ae4b76b686ea3ad54f9e6919bfa4845389f7b6a32f4a4e2f36                                                                                                                                                      0.0s
 => [2/6] RUN sudo apt-get -qq update     && sudo apt-get -qq install -y --no-install-recommends        vim        nano        less        g++-arm-linux-gnueabihf        cmake                                                                                           60.6s
 => [3/6] RUN git clone https://github.com/conan-io/training                                                                                                                                                                                                               3.7s 
 => [4/6] RUN conan profile new default --detect --force                                                                                                                                                                                                                  11.0s 
 => [5/6] RUN conan profile update settings.compiler.libcxx=libstdc++11 default                                                                                                                                                                                            5.7s 
 => [6/6] WORKDIR /home/conan/training                                                                                                                                                                                                                                     0.0s 
 => exporting to image                                                                                                                                                                                                                                                     0.8s 
 => => exporting layers                                                                                                                                                                                                                                                    0.8s 
 => => writing image sha256:9eebc359abf5a26dcce8f2c873586023da340f13b2141f9297847937892375d6                                                                                                                                                                               0.0s 
 => => naming to docker.io/uilianries/gcc9-armv7

% docker run --rm --platform=linux/amd64 uilianries/gcc9-armv7  arm-linux-gnueabihf-gcc --version 
arm-linux-gnueabihf-gcc (Ubuntu 9.4.0-1ubuntu1~20.04.1) 9.4.0
Copyright (C) 2019 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.