scripts/build_utils: setup_pbuilder_for_old_gcc() installs requested version

scripts/build_utils: setup_pbuilder_for_old_gcc() installs requested version

ubuntu noble is special in that we gcc-14 is available but gcc-13 is the
default. before using update-alternatives to prefer gcc-14, we need to
make sure it's installed

copy the relevant bit from setup_pbuilder_for_new_gcc()'s hook
D05install-new-gcc to make sure the requested version is installed
before running the D10update-gcc-alternatives hook

Signed-off-by: Casey Bodley <cbodley@redhat.com>