ci(security): give pip-audit the same registry-outage retry as npm

pip-audit queries PyPI's advisory API and exits non-zero when it cannot
reach it, exactly as `npm audit` does — the same class of outage that
reddened #409 would have failed the Python half too.

Both now go through .github/scripts/audit-with-retry.sh, which retries
only when the output names a transport or availability failure and lets
a real finding fail on the first attempt, unretried. The npm loop added
in the previous commit is folded into it.

ha-relevant: no

.github/scripts/audit-with-retry.sh

@@ -0,0 +1,38 @@
+#!/usr/bin/env bash
+#
+# Run a dependency audit, retrying only when the registry could not be reached.
+#
+# Both `npm audit` and `pip-audit` exit non-zero for two very different reasons:
+# a real advisory, and a registry that would not answer. Only the second is
+# worth a retry — the audit endpoints 503 often enough to redden PRs that
+# changed no dependency at all. An advisory fails on the first attempt, so a
+# vulnerability can never be retried into a pass.
+#
+# Usage: audit-with-retry.sh <command> [args...]
+
+set -uo pipefail
+
+ATTEMPTS=${AUDIT_ATTEMPTS:-3}
+DELAY=${AUDIT_RETRY_DELAY:-30}
+
+# Transport and availability failures, from both npm and pip-audit/urllib3.
+NETWORK_FAILURE='audit endpoint returned an error|service unavailable|max retries exceeded|connectionerror|readtimeout|read timed out|temporary failure in name resolution|50[234] server error|etimedout|econnreset|enotfound|socket hang up|connection reset|remotedisconnected|urlopen error|timeouterror'
+
+for attempt in $(seq 1 "$ATTEMPTS"); do
+  if out=$("$@" 2>&1); then
+    echo "$out"
+    exit 0
+  fi
+  echo "$out"
+
+  if ! grep -qiE "$NETWORK_FAILURE" <<<"$out"; then
+    echo "::error::$1 reported findings — see the output above"
+    exit 1
+  fi
+
+  echo "::warning::$1 could not reach its registry (attempt $attempt/$ATTEMPTS)"
+  if [ "$attempt" -lt "$ATTEMPTS" ]; then sleep "$DELAY"; fi
+done
+
+echo "::error::$1 could not reach its registry after $ATTEMPTS attempts"
+exit 1