ITHttpAnnotation test fails with HttpResponseException in JDK 21

[mpeddada1]

Discovered in #2694. The ITHttpAnnotationTest fails with the following error:

Error:  Tests run: 4, Failures: 0, Errors: 1, Skipped: 0, Time elapsed: 0.072 s <<< FAILURE! -- in com.google.showcase.v1beta1.it.ITHttpAnnotation
Error:  com.google.showcase.v1beta1.it.ITHttpAnnotation.testComplianceGroup[Compliance Group Name: Fully working conversions, no resources] -- Time elapsed: 0.014 s <<< ERROR!
com.google.api.gax.rpc.InvalidArgumentException: Bad Request
	at com.google.api.gax.rpc.ApiExceptionFactory.createException(ApiExceptionFactory.java:52)
	at com.google.api.gax.httpjson.HttpJsonApiExceptionFactory.createApiException(HttpJsonApiExceptionFactory.java:76)
	at com.google.api.gax.httpjson.HttpJsonApiExceptionFactory.create(HttpJsonApiExceptionFactory.java:54)
	at 

. . .
Caused by: com.google.api.client.http.HttpResponseException: 400 Bad Request
POST http://localhost:7469/v1beta1/repeat:body
{"error":{"code":400,"message":"error reading body params '*': proto: syntax error (line 1:513): invalid value \u0000","details":null,"Body":"","Header":null,"Errors":null}}
	at com.google.api.client.http.HttpResponseException$Builder.build(HttpResponseException.java:293)
	at com.google.api.client.http.HttpRequest.execute(HttpRequest.java:1118)
	at com.google.api.gax.httpjson.HttpRequestRunnable.run(HttpRequestRunnable.java:115)
	... 6 more

Note that this test doesn't fail consistently. Running the same test 20 times shows the test failing 15/20 times.

The exception is being thrown at HttpRequest#execute.