Bump actions/checkout from 5 to 6 #156

Job	Run time
shellcheck	7s
usage-as-proxy	14s
eval-bash	13s
install-pkgx (macos-latest)	14s
install-pkgx (ubuntu-latest)	15s
sudo-not-required	16s
no-dirs (/usr/local)	13s
sudo-required	13s
pkgm	13s
no-dirs (/usr/local/bin)	15s
eval-zsh	25s
upgrades	18s
eval-posix-sh	13s
windows	26s
linuxen (ubuntu:jammy)	25s
linuxen (ubuntu:noble)	23s
multiple-apply-is-ok	13s
linuxen (archlinux:latest)	27s
linuxen (debian:bookworm-slim)	22s
linuxen (ubuntu:focal)	25s
linuxen (fedora:latest)	25s
linuxen (debian:buster-slim)	23s
linuxen (debian:bullseye-slim)	22s
	7m 0s

Provide feedback