Disable MSAN testing for cache-key unit tests.

This is an existing issue with the compilation cache tests.
The refactoring of the cache key generation part into a separate
file requires tagging the refactored tests also.

PiperOrigin-RevId: 551972670

tests/BUILD

@@ -927,6 +927,9 @@ jax_test(
 jax_test(
     name = "cache_key_test",
     srcs = ["cache_key_test.py"],
+    backend_tags = {
+        "tpu": ["nomsan"],  # TODO(b/213388298): this test fails msan.
+    },
     deps = ["//jax:cache_key"],
 )