fix(ci): add apt update before libffi

Author: csegarragonz

.github/workflows/tests.yml

@@ -37,7 +37,10 @@ jobs:
       - name: "Build libfaasmpi"
         run: ./bin/inv_wrapper.sh libfaasmpi
       - name: "Build libffi"
-        run: ./bin/inv_wrapper.sh libffi
+        run: |
+          # For some reason, libffi necessitates running apt update.
+          apt update
+          ./bin/inv_wrapper.sh libffi
       - name: "Build libfake"
         run: ./bin/inv_wrapper.sh libfake
       - name: "Build libemscripten"