fix: remove custom proxy handling (#143)

Undici has added native support for proxy handling, so it is no longer necessary for us to have our own custom proxy handling.

Reverts #102 and resolves #134.

package.json

@@ -18,8 +18,7 @@
     "@actions/core": "^1.11.1",
     "@octokit/auth-app": "^7.2.1",
     "@octokit/request": "^9.2.2",
-    "p-retry": "^6.2.1",
-    "undici": "^7.8.0"
+    "p-retry": "^6.2.1"
   },
   "devDependencies": {
     "@octokit/openapi": "^19.1.0",
@@ -30,6 +29,7 @@
     "esbuild": "^0.25.8",
     "execa": "^9.6.0",
     "open-cli": "^8.0.0",
+    "undici": "^7.13.0",
     "yaml": "^2.8.1"
   },
   "release": {