Fix benchmarks not running on PRs (#1731)

Address an issue introduced in #1722 where benchmark workflows would not
run on PRs (enabled when setting the "performance" label).

### Does this change impact existing behavior?

No, CI only.

### Does this change need a changelog entry? Does it require a version
change?

No.

---

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under the terms of the Apache 2.0 license and I agree to the terms of
the [Developer Certificate of Origin
(DCO)](https://developercertificate.org/).

Signed-off-by: Alessandro Passaro <alexpax@amazon.co.uk>

Author: passaro

.github/workflows/bench_pr.yml

@@ -6,7 +6,7 @@ on:
 
 permissions:
   id-token: write
-  contents: read
+  contents: write # required by bench.yml and bench_s3express.yml even if we don't actually publish the results to gh-pages for PRs
 
 jobs:
   integration: