fix: api key copy (#46159)

## TL;DR 

a smol fix regarding masked secret API key text being copied when reveal
fails

## ref:

- closes https://github.com/supabase/supabase/issues/46157

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## Summary by CodeRabbit

* **Bug Fixes**
* Improved secret API key copy behavior to handle edge cases where the
reveal operation returns no value, preventing unintended fallback
behavior.

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apps/studio/components/interfaces/APIKeys/ApiKeyPill.tsx

@@ -76,7 +76,7 @@ export function ApiKeyPill({
       return key ?? ''
     } catch {
       toast.error('Failed to copy secret API key')
-      return apiKey.api_key
+      return ''
     }
   }