fix: remove timestamp option from osx-sign (default handles it)

codesign rejects --timestamp=true, needs --timestamp with no value.
@electron/osx-sign adds --timestamp by default, so remove the explicit opt.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: nunocoracao

.github/workflows/release.yml

@@ -231,7 +231,6 @@ jobs:
                     hardenedRuntime: true,
                     entitlements: path.join(process.cwd(), 'entitlements.mac.plist'),
                     'entitlements-inherit': path.join(process.cwd(), 'entitlements.mac.plist'),
-                    timestamp: true,
                   }),
                 });
                 console.log('Code signing complete.');