build: upgrade Java microgenerator to v2.2.1

# v2.2.1

## Bug Fixes
- gax batching regression (#863) (3a6f168)

# v2.2.0

## Features
- Add REST AIP-151 LRO suport (cb1b534)
- enable self signed JWT for http (#850) (aba0ec0)
- Implement DIREGAPIC LRO annotations (#832) (d7b29e0)
- REGAPIC initial implementation (#824) (fdcfe70)
- REGAPIC Multitransport implementation (grpc+rest) (#833) (445daf4)

## Bug Fixes
- [bazel] fix rest transport handling in assembly rule (#835) (92f7c1c)
- DIREGAPIC LRO generated tests logic (#838) (8ae8e6f)
- fix diregapic-lro logic (#834) (957f69a)

PiperOrigin-RevId: 405492216

WORKSPACE

@@ -202,7 +202,7 @@ grpc_java_repositories()
 
 # Java microgenerator.
 # Must go AFTER java-gax, since both java gax and gapic-generator are written in java and may conflict.
-_gapic_generator_java_version = "2.1.0"
+_gapic_generator_java_version = "2.2.1"
 
 http_archive(
     name = "gapic_generator_java",