chore: ignore failing VpcFlowLogsServiceClientHttpJsonTest unit tests in network management

[mpeddada1]

In https://github.com/googleapis/google-cloud-java/pull/11058#issuecomment-2299496737, these tests were failing due to the failing error:

2024-08-20T18:29:08.1770438Z 18:29:08:140 [INFO] -------------------------------------------------------
2024-08-20T18:29:08.1774835Z 18:29:08:140 [INFO]  T E S T S
2024-08-20T18:29:08.1776173Z 18:29:08:140 [INFO] -------------------------------------------------------
2024-08-20T18:29:09.1013370Z 18:29:09:101 [INFO] Tests run: 64, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 2.282 s -- in com.google.cloud.networksecurity.v1beta1.NetworkSecurityClientTest
2024-08-20T18:29:09.1016245Z 18:29:09:101 [INFO] Running com.google.cloud.networksecurity.v1.NetworkSecurityClientTest
2024-08-20T18:29:10.1205457Z 18:29:10:120 [ERROR] Tests run: 32, Failures: 0, Errors: 3, Skipped: 0, Time elapsed: 4.437 s <<< FAILURE! -- in com.google.cloud.networkmanagement.v1beta1.VpcFlowLogsServiceClientHttpJsonTest
2024-08-20T18:29:10.1208480Z 18:29:10:120 [ERROR] com.google.cloud.networkmanagement.v1beta1.VpcFlowLogsServiceClientHttpJsonTest.getIamPolicyTest -- Time elapsed: 0.209 s <<< ERROR!
2024-08-20T18:29:10.1210337Z com.google.api.gax.rpc.NotFoundException: 
2024-08-20T18:29:10.1211123Z com.google.api.client.http.HttpResponseException: 404
2024-08-20T18:29:10.1212990Z GET https://networkmanagement.googleapis.com:443/v1beta1/GetIamPolicyRequest-1527610370:getIamPolicy?$alt=json;enum-encoding%3Dint
2024-08-20T18:29:10.1214954Z Method not found for path 'https:///v1beta1/GetIamPolicyRequest-1527610370:getIamPolicy'
2024-08-20T18:29:10.1216496Z 	at com.google.api.gax.rpc.ApiExceptionFactory.createException(ApiExceptionFactory.java:90)

This is a known issue (https://github.com/googleapis/sdk-platform-java/issues/1839). The current workaround is to ignore these tests. This PR emulates https://github.com/googleapis/google-cloud-java/pull/10543/files