fix: plugins/events-backend-module-github/package.json to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-JS-WEBPACK-15235959
- https://snyk.io/vuln/SNYK-JS-WEBPACK-15235969
- https://snyk.io/vuln/SNYK-JS-QS-15268416

Author: snyk-bot

plugins/events-backend-module-github/package.json

@@ -35,9 +35,9 @@
     "postpack": "backstage-cli package postpack"
   },
   "dependencies": {
-    "@backstage/backend-plugin-api": "workspace:^",
-    "@backstage/config": "workspace:^",
-    "@backstage/plugin-events-node": "workspace:^",
+    "@backstage/backend-plugin-api": "0.6.19",
+    "@backstage/config": "0.1.1",
+    "@backstage/plugin-events-node": "0.2.9",
     "@octokit/webhooks-methods": "^3.0.0",
     "winston": "^3.2.1"
   },