Improve comment to clarify use of gmdate() for UTC consistency

Co-authored-by: swissspidy <841956+swissspidy@users.noreply.github.com>

Author: Copilot

src/UpdatePoCommand.php

@@ -87,7 +87,8 @@ public function __invoke( $args, $assoc_args ) {
 				Merge::ADD | Merge::REMOVE | Merge::COMMENTS_THEIRS | Merge::EXTRACTED_COMMENTS_THEIRS | Merge::REFERENCES_THEIRS | Merge::DOMAIN_OVERRIDE
 			);
 
-			// Update PO-Revision-Date to current date and time.
+			// Update PO-Revision-Date to current date and time in UTC.
+			// Uses gmdate() for consistency across different server timezones.
 			$po_translations->setHeader( 'PO-Revision-Date', gmdate( 'Y-m-d\TH:i:sP' ) );
 
 			if ( ! $po_translations->toPoFile( $file->getPathname() ) ) {