ci: sanitize the workflow file (#1747)

Author: rawalexe

.github/workflows/maven.yml

@@ -85,13 +85,16 @@ jobs:
           sudo mvn -ntp -U -f src/test/greengrass-nucleus-benchmark install
         if: matrix.os == 'ubuntu-latest'
       - name: Save PR number
+        env:
+          PR_NUMBER: ${{ github.event.number }}
+          PR_SHA: ${{ github.event.pull_request.head.sha }}
         run: |
           mkdir -p ./pr/jacoco-report
           mkdir -p ./pr/japicmp
           mkdir -p target/japicmp
           mkdir -p target/jacoco-report
-          echo ${{ github.event.number }} > ./pr/NR
-          echo ${{ github.event.pull_request.head.sha }} > ./pr/SHA
+          echo "$PR_NUMBER" > ./pr/NR
+          echo "$PR_SHA" > ./pr/SHA
           cp -R target/japicmp/default-cli.xml ./pr/japicmp/default-cli.xml
           cp target/jacoco-report/cobertura.xml ./pr/jacoco-report/cobertura.xml
           cp target/jacoco-report/cobertura-it.xml ./pr/jacoco-report/cobertura-it.xml