Update step-security/harden-runner action to v2.15.0

Author: renovate[bot]

.github/workflows/testing.yml

@@ -32,7 +32,7 @@ jobs:
         go: ["1.24", "1.25" ]
     steps:
       - name: Harden Runner
-        uses: step-security/harden-runner@63c24ba6bd7ba022e95695ff85de572c04a18142 # v2.7.0
+        uses: step-security/harden-runner@a90bcbc6539c36a85cdfeb73f7e2f433735f215b # v2.15.0
         with:
           egress-policy: audit
           disable-telemetry: true