chore:always use dotnet 6 for format checking

Author: ajewellamz

.github/actions/polymorph_codegen/action.yml

@@ -96,6 +96,8 @@ runs:
       shell: bash
       run: |
         echo "PROJECT_DEPENDENCIES=${{ inputs.update-and-regenerate-mpl != 'true' && 'PROJECT_DEPENDENCIES=' || '' }}" >> $GITHUB_OUTPUT
+      run: |
+        dotnet --version
 
     - name: Regenerate Dafny code using smithy-dafny
       # Unfortunately Dafny codegen doesn't work on Windows:

.github/workflows/ci_codegen.yml

@@ -48,6 +48,9 @@ jobs:
         with:
           dotnet-version: ${{ matrix.dotnet-version }}
 
+      - name: Create temporary global.json
+        run: echo '{"sdk":{"rollForward":"latestFeature","version":"6.0.0"}}' > ./global.json
+
       - name: Setup Java 17 for codegen
         uses: actions/setup-java@v3
         with: