Add Rush change file for MutabilityWithReadOnly performance fix

Co-authored-by: mikeharder <9459391+mikeharder@users.noreply.github.com>

Author: Copilot

common/changes/@microsoft.azure/openapi-validator-rulesets/copilot-mutability-readonly-performance-fix_2026-01-29-05-58.json

@@ -0,0 +1,10 @@
+{
+  "changes": [
+    {
+      "packageName": "@microsoft.azure/openapi-validator-rulesets",
+      "comment": "Optimize MutabilityWithReadOnly rule to prevent out-of-memory issues by filtering in JSONPath given clause (fixes #812)",
+      "type": "patch"
+    }
+  ],
+  "packageName": "@microsoft.azure/openapi-validator-rulesets"
+}