Use an intermediate environment variable (#95)

Adhering to https://docs.github.com/en/actions/reference/security/secure-use#use-an-intermediate-environment-variable

Aligns with https://github.com/aws-observability/aws-otel-go/pull/280/files

Author: thpierce

.github/workflows/soak-testing.yml

@@ -13,7 +13,7 @@ on:
       test_duration_minutes:
         description: 'The duration of the Soak Tests in minutes.'
         required: true
-        default: 300
+        default: "300"
   schedule:
     - cron: '0 15 * * *'
 env:
@@ -53,16 +53,20 @@ jobs:
     # MARK: - GitHub Workflow Event Type Specific Values
 
       - name: Use INPUT as commit SHA
+        env:
+          TARGET_SHA: ${{ github.event.inputs.target_commit_sha }}
         if: ${{ github.event_name == 'workflow_dispatch' }}
         run: |
-          echo "TARGET_SHA=${{ github.event.inputs.target_commit_sha }}" | tee --append $GITHUB_ENV;
+          echo "$TARGET_SHA" | tee --append $GITHUB_ENV;
       - name: Use LATEST as commit SHA
         if: ${{ github.event_name != 'workflow_dispatch' }}
         run: |
           echo "TARGET_SHA=${{ github.sha }}" | tee --append $GITHUB_ENV;
       - name: Configure Performance Test Duration
+        env:
+          TEST_DURATION_MINUTES: ${{ github.event.inputs.test_duration_minutes || env.DEFAULT_TEST_DURATION_MINUTES }}
         run: |
-          echo "TEST_DURATION_MINUTES=${{ github.event.inputs.test_duration_minutes || env.DEFAULT_TEST_DURATION_MINUTES }}" | tee --append $GITHUB_ENV;
+          echo "$TEST_DURATION_MINUTES" | tee --append $GITHUB_ENV;
       - name: Clone This Repo @ ${{ env.TARGET_SHA }}
         uses: actions/checkout@v3
         with: