Update dependency release-plan to ^0.15.0

Author: renovate[bot]

package.json

@@ -89,7 +89,7 @@
     "prettier": "^3.0.3",
     "qunit": "^2.20.0",
     "qunit-dom": "^2.0.0",
-    "release-plan": "^0.8.0",
+    "release-plan": "^0.15.0",
     "stylelint": "^15.11.0",
     "stylelint-config-standard": "^34.0.0",
     "stylelint-prettier": "^4.0.2",