CI: gentoo: fix profile 23.0 migration dropping default fortran

We need this for scalapack -> virtual/mpi -> openmpi

See https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=a1b86025be85171281811eaced7b342fbdfdb591

We now get an immediate, very nicely readable error that the USE flag is
necessary. For our use cases, there's no reason not to globally enable
it.

ci/ciimage/gentoo/install.sh

@@ -114,6 +114,9 @@ cat <<-EOF >> /etc/portage/make.conf
 	EMERGE_DEFAULT_OPTS="\${EMERGE_DEFAULT_OPTS} --autounmask-write --autounmask-continue --autounmask-keep-keywords=y --autounmask-use=y"
 	EMERGE_DEFAULT_OPTS="\${EMERGE_DEFAULT_OPTS} --binpkg-respect-use=y"
 
+	# Fortran is no longer enabled by default in 23.0, but we do need and use it.
+	USE="\${USE} fortran"
+
 	FEATURES="\${FEATURES} parallel-fetch parallel-install -merge-sync"
 	FEATURES="\${FEATURES} getbinpkg binpkg-request-signature"