chore: always use dotnet 6 for format checking. (#1403)

* chore:always use dotnet 6 for format checking

Author: ajewellamz

.github/actions/polymorph_codegen/action.yml

@@ -97,6 +97,11 @@ runs:
       run: |
         echo "PROJECT_DEPENDENCIES=${{ inputs.update-and-regenerate-mpl != 'true' && 'PROJECT_DEPENDENCIES=' || '' }}" >> $GITHUB_OUTPUT
 
+    - name: Print dotnet version
+      shell: bash
+      run: |
+        dotnet --version
+
     - name: Regenerate Dafny code using smithy-dafny
       # Unfortunately Dafny codegen doesn't work on Windows:
       # https://github.com/smithy-lang/smithy-dafny/issues/317

.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: