gitlab-ci: Install process to global pkgdb before starting build

This is an attempt to mitigate #17480 by ensuring that a functional version of
the process library is available before attempting the build.

.gitlab/win32-init.sh

@@ -45,3 +45,5 @@ if [ ! -e $toolchain/bin/alex ]; then
     cp $APPDATA/cabal/bin/alex $toolchain/bin
 fi
 
+# Install new process to mitigate #17480.
+cabal install libraries/process