Revert "Allow bare bun in packageManager (SchemaStore#5589)" (SchemaStore#5599)

Author: hyperupcall

src/negative_test/package/package-manager-bun-substring.json

@@ -797,7 +797,7 @@
     "packageManager": {
       "description": "Defines which package manager is expected to be used when working on the current project. This field is currently experimental and needs to be opted-in; see https://nodejs.org/api/corepack.html",
       "type": "string",
-      "pattern": "^((npm|pnpm|yarn|bun)@\\d+\\.\\d+\\.\\d+(-.+)?|bun)$"
+      "pattern": "(npm|pnpm|yarn|bun)@\\d+\\.\\d+\\.\\d+(-.+)?"
     },
     "engines": {
       "type": "object",