only run codspeed benchmarks on PRs labelled 'benchmark' (zarr-developers#3673)

* only run codspeed benchmarks on PRs labelled 'benchmark'

* changelog

* rename changelog

Author: d-v-b

.github/workflows/codspeed.yml

@@ -5,6 +5,7 @@ on:
     branches:
       - "main"
   pull_request:
+    types: [labeled, synchronize]
   # `workflow_dispatch` allows CodSpeed to trigger backtest
   # performance analysis in order to generate initial data.
   workflow_dispatch:
@@ -16,6 +17,11 @@ jobs:
   benchmarks:
     name: Run benchmarks
     runs-on: codspeed-macro
+    # Only run benchmarks for: pushes to main, manual triggers, or PRs with 'benchmark' label
+    if: |
+      github.event_name == 'push' ||
+      github.event_name == 'workflow_dispatch' ||
+      (github.event_name == 'pull_request' && contains(github.event.pull_request.labels.*.name, 'benchmark'))
     steps:
     - uses: actions/checkout@v6
       with:

changes/3673.misc.md

@@ -0,0 +1 @@
+Benchmark CI now only runs for PRs with the `benchmark` label, reducing CodSpeed credit usage.