ci: Use GITHUB_OUTPUT envvar instead of set-output command

`save-state` and `set-output` commands used in GitHub Actions are deprecated and [GitHub recommends using environment files](https://github.blog/changelog/2023-07-24-github-actions-update-on-save-state-and-set-output-commands/).

This PR updates the usage of `::set-output` to `"$GITHUB_OUTPUT"`

Instructions for envvar usage from GitHub docs:

https://docs.github.com/en/actions/using-workflows/workflow-commands-for-github-actions#setting-an-output-parameter

.github/workflows/ci.yaml

@@ -20,7 +20,7 @@ jobs:
         env:
           GCP_PROJECT_ID: ${{ secrets.GCP_PROJECT_ID }}
         if: "${{ env.GCP_PROJECT_ID != '' }}"
-        run: echo "::set-output name=defined::true"
+        run: echo "defined=true" >> "$GITHUB_OUTPUT"
 
   lint:
     runs-on: ubuntu-latest

.github/workflows/go-sample-test.yaml

@@ -19,7 +19,7 @@ jobs:
         env:
           GCP_PROJECT_ID: ${{ secrets.GCP_PROJECT_ID }}
         if: "${{ env.GCP_PROJECT_ID != '' }}"
-        run: echo "::set-output name=defined::true"
+        run: echo "defined=true" >> "$GITHUB_OUTPUT"
   sample-test:
     needs: [check-env]
     if: needs.check-env.outputs.has-key == 'true'

.github/workflows/integration.yaml

@@ -34,7 +34,7 @@ jobs:
         env:
           GCP_PROJECT_ID: ${{ secrets.GCP_PROJECT_ID }}
         if: "${{ env.GCP_PROJECT_ID != '' }}"
-        run: echo "::set-output name=defined::true"
+        run: echo "defined=true" >> "$GITHUB_OUTPUT"
   integration-test:
     needs: [check-env]
     if: needs.check-env.outputs.has-key == 'true'

.github/workflows/ycsb.yaml

@@ -14,7 +14,7 @@ jobs:
         env:
           GCP_PROJECT_ID: ${{ secrets.GCP_PROJECT_ID }}
         if: "${{ env.GCP_PROJECT_ID != '' }}"
-        run: echo "::set-output name=defined::true"
+        run: echo "defined=true" >> "$GITHUB_OUTPUT"
   ycsb-benchmark:
     needs: [check-env]
     if: needs.check-env.outputs.has-key == 'true'