fix: plugins/proxy-backend/package.json to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-JS-DIFF-14917201
- https://snyk.io/vuln/SNYK-JS-BACKSTAGEBACKENDPLUGINAPI-15054291
- https://snyk.io/vuln/SNYK-JS-LODASH-15053838
- https://snyk.io/vuln/SNYK-JS-LODASHES-15053836

Author: snyk-io[bot]

plugins/proxy-backend/package.json

@@ -33,9 +33,9 @@
     "clean": "backstage-cli package clean"
   },
   "dependencies": {
-    "@backstage/backend-common": "workspace:^",
-    "@backstage/backend-plugin-api": "workspace:^",
-    "@backstage/config": "workspace:^",
+    "@backstage/backend-common": "0.25.0",
+    "@backstage/backend-plugin-api": "1.6.1",
+    "@backstage/config": "0.1.1",
     "@types/express": "^4.17.6",
     "express": "^4.17.1",
     "express-promise-router": "^4.1.0",