Don't set packageManager default via action.yml

We need to distinguish between when the value is and isn't set in order to perform inference based on lockfile and only fallback to the default of npm if inference fails.

.changeset/dirty-poets-swim.md

@@ -0,0 +1,5 @@
+---
+"wrangler-action": patch
+---
+
+Fixed the package manager not being inferred based on lockfile when the `packageManager` input isn't set.

action.yml

@@ -42,6 +42,5 @@ inputs:
     description: "A string of environment variable names, separated by newlines. These will be bound to your Worker using the values of matching environment variables declared in `env` of this workflow."
     required: false
   packageManager:
-    description: "The package manager you'd like to use to install and run wrangler. If not specified, a value will be inferred based on the presence of a lockfile. Valid values: [npm, pnpm, yarn, bun]"
+    description: "The package manager you'd like to use to install and run wrangler. If not specified, the preferred package manager will be inferred based on the presence of a lockfile or fallback to using npm if no lockfile is found. Valid values are `npm` | `pnpm` | `yarn` | `bun`."
     required: false
-    default: npm