ci: Install Gitaly gems even when Gitaly binaries are cached

Signed-off-by: Rémy Coutable <remy@rymai.me>

scripts/gitaly-test-build

@@ -18,6 +18,8 @@ class GitalyTestBuild
     # If we have the binaries from the cache, we can skip building them again
     if File.exist?(tmp_tests_gitaly_bin_dir)
       GitalySetup::LOGGER.debug "Gitaly binary already built. Skip building...\n"
+      # We still need to install the gems in that case
+      install_gitaly_gems
     else
       abort 'gitaly build failed' unless build_gitaly
     end