ci: use stable fedora to fix ci
Rawhide is breaking the introspecting build with a permission to read error.
ldd: error: you do not have read permission for `/builds/victortoso/grilo/_build/tmp-introspectba6itfp6/Grl-0.3'
That is a temporary folder created by meson (0.55.0-2) but I think the issue is in the new python 3.9. I could not reproduce locally but for now, let's fix CI for grilo and grilo-plugins (due subprojects)