Validate assembler content source configs as part of our PR builds (#1301)

Author: Mpdreamz

.github/workflows/pr.yml

@@ -14,7 +14,7 @@ env:
   NUGET_PACKAGES: ${{ github.workspace }}/.nuget/packages
 
 jobs:
-  validate-navigation:
+  validate-assembler:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
@@ -23,9 +23,12 @@ jobs:
         id: bootstrap
         uses: ./.github/actions/bootstrap
 
-      - name: Build
+      - name: Validate Navigation
         run: dotnet run --project src/tooling/docs-assembler -c release -- navigation validate
 
+      - name: Validate Content Sources
+        run: dotnet run --project src/tooling/docs-assembler -c release -- content-source validate
+
   build-lambda:
     uses: ./.github/workflows/build-link-index-updater-lambda.yml