Add flatpak-runtime-config to the srpm-buildroot group
    
    When we are building a SRPM that in a module that buildrequires
    flatpak-runtime, already built packages will be in the repositories
    that are used to install the "srpm-build" packages. We might end
    up with libraries in /app/lib[64] because of this, so we need
    flatpak-runtime-config.
    
    For example, the libreoffice build rebuilds libssh - this is a
    dependency of curl, so having a rebuilt libssh without having
    /app/lib[64] in the path breaks 'rhpkg-simple sources'.
    
    Also include flatpak-rpm-macros - we don't expect that any macros
    in there would change how a SRPM is built, but if they *do* change
    how a SPRM is built, then we want them installed when building the
    SRPM.