Make typepal checkout depend on whether a version was specified

Author: sungshik

.github/workflows/run-integration-test.yml

@@ -49,6 +49,7 @@ jobs:
           path: 'deps/rascal'
 
       - uses: actions/checkout@v4
+        if: ${{ inputs.typepal_version != '' }}
         name: 'Checkout typepal (${{ inputs.typepal_version }})'
         with:
           repository: 'usethesource/typepal'