CI: use g++ 9 for android builds

Ubuntu 20.04 removed package of g++ 8. Therefore,
version 9 is used.

Signed-off-by: Patryk Wrobel <183546751+pwrobeldev@users.noreply.github.com>

Author: pwrobeldev

.github/workflows/functional-tests.yml

@@ -76,7 +76,7 @@ jobs:
       - name: Install GCC
         uses: egor-tensin/setup-gcc@v1
         with:
-          version: 8
+          version: 9
       - name: Install CMake
         uses: jwlawson/actions-setup-cmake@v1.7
         with:
@@ -138,7 +138,7 @@ jobs:
       - name: Install GCC
         uses: egor-tensin/setup-gcc@v1
         with:
-          version: 8
+          version: 9
       - name: Install CMake
         uses: jwlawson/actions-setup-cmake@v1.7
         with: