Added codecov token in cleartext

The Codecov upload token will be no longer optional in v4 of the action,
so it will be necessary to adjust the workflow to provide the
token to the action at the same time as the bump. Doing so is a good
idea anyway because, although supported in v3, the lack of a token
was causing periodic spurious coverage data upload failures. That
was done already in the Arduino CLI repo (arduino/arduino-cli#2129)
and the approach used there has passed the test of time with flying
colors.

The workflow does currently use the token input of the action, but
it uses the flawed approach of storing it in a secret, which would
cause the workflow run to fail on any PR submitted from a fork after
the action bump. So the workflow must be updated to use the system
implemented in the Arduino CLI workflow.

Author: cmaglie

.github/workflows/test-go-task.yml

@@ -92,11 +92,25 @@ jobs:
           GO_MODULE_PATH: ${{ matrix.module.path }}
         run: task go:test
 
+      # A token is used to avoid intermittent spurious job failures caused by rate limiting.
+      - name: Set up Codecov upload token
+        run: |
+          if [[ "${{ github.repository }}" == "arduino/pluggable-discovery-protocol-handler" ]]; then
+            # In order to avoid uploads of data from forks, only use the token for runs in this repo.
+            # Token is intentionally exposed.
+            # See: https://community.codecov.com/t/upload-issues-unable-to-locate-build-via-github-actions-api/3954
+            CODECOV_TOKEN="d2497f03-291d-4e0c-9d31-d94614ed7c16"
+          else
+            # codecov/codecov-action does unauthenticated upload if empty string is passed via the `token` input.
+            CODECOV_TOKEN=""
+          fi
+          echo "CODECOV_TOKEN=$CODECOV_TOKEN" >> "$GITHUB_ENV"
+
       - name: Send unit tests coverage to Codecov
         if: runner.os == 'Linux'
         uses: codecov/codecov-action@v3
         with:
+          token: ${{ env.CODECOV_TOKEN }}
           file: ${{ matrix.module.path }}coverage_unit.txt
           flags: ${{ matrix.module.codecov-flags }}
-          token: ${{ secrets.CODECOV_TOKEN }}
           fail_ci_if_error: ${{ github.repository == 'arduino/pluggable-discovery-protocol-handler' }}