Add pkg-config install in CI (should fix issues)

Installing pkg-config in the workflowconfig file should fix configure
issues, and allow the CI to succeed.

.github/workflows/vfc_test_workflow.yml

@@ -25,7 +25,7 @@ jobs:
         run: |
           ln -s /usr/bin/python3 /usr/bin/python
           apt update
-          apt -y install emacs
+          apt -y install emacs pkg-config
 
       - name: Run tests
         run: vfc_ci test -g -r