Normalize workflow_call secret name to APIKey

The reusable workflow declared the gallery secret as APIKEY while every usage, the nested Publish-Module workflow, the test callers, and the README use APIKey. GitHub secret names are case-insensitive so publishing worked, but this removes the inconsistency Copilot flagged.

Author: MariusStorhaug

.github/workflows/workflow.yml

@@ -3,7 +3,7 @@ name: Process-PSModule
 on:
   workflow_call:
     secrets:
-      APIKEY:
+      APIKey:
         description: The API key for the PowerShell Gallery.
         required: true
       TestData: