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

Author: renovate[bot]

.github/workflows/validate.yaml

@@ -17,7 +17,7 @@ jobs:
       YQ_VERSION: 3.4.3
     steps:
       - name: Harden Runner
-        uses: step-security/harden-runner@20cf305ff2072d973412fa9b1e3a4f227bda3c76 # v2.14.0
+        uses: step-security/harden-runner@a90bcbc6539c36a85cdfeb73f7e2f433735f215b # v2.15.0
         with:
           egress-policy: audit