Reinstate Ubuntu-2004 github actions runner image for nightly tests.

 - This is done because Centos-7, OracleLinux-7 and Scientific-7 are not getting provisioned on the ubuntu-2204 github runner image resulting in nightly job failures. This might be due to the EOL status of EL-7 based images.

Author: shubhamshinde360

.github/workflows/ci.yml

@@ -5,7 +5,7 @@ on:
     branches:
       - "main"
   workflow_dispatch:
-    
+
 jobs:
   Spec:
     uses: "puppetlabs/cat-github-actions/.github/workflows/module_ci.yml@main"
@@ -15,3 +15,5 @@ jobs:
     needs: Spec
     uses: "puppetlabs/cat-github-actions/.github/workflows/module_acceptance.yml@main"
     secrets: "inherit"
+    with:
+      runs_on: "ubuntu-20.04"

.github/workflows/nightly.yml

@@ -14,3 +14,5 @@ jobs:
     needs: Spec
     uses: "puppetlabs/cat-github-actions/.github/workflows/module_acceptance.yml@main"
     secrets: "inherit"
+    with:
+      runs_on: "ubuntu-20.04"