[Release] Fix v1.55 g name (#32879)

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doc/g_stands_for.md

@@ -54,4 +54,4 @@
 - 1.52 'g' stands for ['gribkoff'](https://github.com/grpc/grpc/tree/v1.52.x)
 - 1.53 'g' stands for ['glockenspiel'](https://github.com/grpc/grpc/tree/v1.53.x)
 - 1.54 'g' stands for ['gracious'](https://github.com/grpc/grpc/tree/v1.54.x)
-- 1.55 'g' stands for ['gracious'](https://github.com/grpc/grpc/tree/master)
+- 1.55 'g' stands for ['grandslam'](https://github.com/grpc/grpc/tree/master)