ci: update Codecov action to v5 (#47)

Author: marten-seemann

.github/workflows/unit.yml

@@ -30,8 +30,12 @@ jobs:
           GOARCH: 386
         run: go test -v -cover
       - name: Upload coverage to Codecov
-        uses: codecov/codecov-action@v4
+        if: ${{ !cancelled() }}
+        uses: codecov/codecov-action@v5
+        env:
+          OS: ${{ matrix.os }}
+          GO: ${{ matrix.go }}
         with:
-          files: coverage.txt,coverage-root.txt
-          env_vars: OS=${{ matrix.os }}, GO=${{ matrix.go }}
+          files: coverage.txt
+          env_vars: OS,GO
           token: ${{ secrets.CODECOV_TOKEN }}