[ci] Disable monitoring of fork branches

Jobs executing on PRs based on fork branches won't have access to the
secrets required to configure collectors for logs and
metrics. Disabling the collection in the custom action avoids failing
such jobs. This was the behavior prior to the switch to starting
collectors with golang.

Author: maru-ava

.github/actions/run-monitored-tmpnet-cmd/action.yml

@@ -59,12 +59,16 @@ runs:
         GRAFANA_URL: https://grafana-poc.avax-dev.network/d/kBQpRdWnk/avalanche-main-dashboard?orgId=1&refresh=10s&var-filter=is_ephemeral_node%7C%3D%7Cfalse&var-filter=gh_repo%7C%3D%7C${{ inputs.repository_owner }}%2F${{ inputs.repository_name }}&var-filter=gh_run_id%7C%3D%7C${{ inputs.run_id }}&var-filter=gh_run_attempt%7C%3D%7C${{ inputs.run_attempt }}
         GH_JOB_ID: ${{ inputs.job }}
         FILTER_BY_OWNER: ${{ inputs.filter_by_owner }}
+    - name: Warn that collection of metrics and logs will not be performed
+      if: (inputs.prometheus_username != '')
+      shell: bash
+      run: echo "::warning::Monitoring credentials not found. Skipping collector start. Is the PR from a fork branch?"
     - name: Run command
       shell: bash
       # --impure ensures the env vars are accessible to the command
       run: ${{ inputs.run_env }} nix develop --impure --command bash -x ${{ inputs.run }}
       env:
-        TMPNET_START_COLLECTORS: true
+        TMPNET_START_COLLECTORS: ${{ inputs.prometheus_username != '' }}
         LOKI_USERNAME: ${{ inputs.loki_username }}
         LOKI_PASSWORD: ${{ inputs.loki_password }}
         PROMETHEUS_USERNAME: ${{ inputs.prometheus_username }}
@@ -91,7 +95,7 @@ runs:
         if-no-files-found: error
     # TODO(marun) Maybe optionally run these checks in an AfterSuite step?
     - name: Check that logs were collected
-      if: always()
+      if: (inputs.prometheus_username != '')
       shell: bash
       run: go run github.com/ava-labs/avalanchego/tests/fixture/tmpnet/cmd check-logs
       env:
@@ -104,7 +108,7 @@ runs:
         GH_RUN_ATTEMPT: ${{ inputs.run_attempt }}
         GH_JOB_ID: ${{ inputs.job }}
     - name: Check that metrics were collected
-      if: always()
+      if: (inputs.prometheus_username != '')
       shell: bash
       run: go run github.com/ava-labs/avalanchego/tests/fixture/tmpnet/cmd check-metrics
       env: