fix: use correct PASSPHRASE environment variable name

- Change GPG_PASSPHRASE to PASSPHRASE to match GitHub secret name
- Fixes 'map has no entry for key' error during release signing

Author: Trozz

.goreleaser.yml

@@ -65,7 +65,7 @@ signs:
       - ${artifact}
     signature: ${artifact}.sig
     artifacts: checksum
-    stdin: "{{ .Env.GPG_PASSPHRASE }}"
+    stdin: "{{ .Env.PASSPHRASE }}"
 
 # Release configuration
 release: