Re-enable EAToSAImpersonationRest and EAToSAImpersonationGrpc

Currently we see the error, we need to disable it now. I believe it is a temp error, we can try to re-enable it later.

Step #2: [ RUN      ] ExternalAccountImpersonationTest.EAToSAImpersonationRest
Step #2: google/cloud/universe_domain/integration_tests/impersonation_tests.cc:159: Failure
Step #2: Value of: disk
Step #2: Expected: code is equal to OK and message is anything
Step #2:   Actual: 608-byte object <B0-3A 72-00 00-00 00-00 00-00 00-00 00-00 00-00 00-00 00-00 00-00 00-00 00-00 00-00 00-00 00-00 00-00 00-00 00-00 00-00 00-00 00-00 00-00 00-00 00-00 00-00 00-00 00-00 00-00 00-00 00-00 00-00 ... 00-00 00-00 00-00 00-00 00-00 00-00 00-00 00-00 00-00 00-00 00-00 00-00 00-00 00-00 00-00 00-00 00-00 00-00 00-00 00-00 00-00 00-00 00-00 00-00 00-00 00-00 00-00 00-00 00-00 00-00 00-00 00-00>, whose status is INVALID_ARGUMENT: Permanent error, with a last message of {"error":"invalid_grant","error_description":"Error connecting to the given credential's issuer."} error_info={reason=, domain=, metadata={gcloud-cpp.retry.function=ListDisks, gcloud-cpp.retry.reason=permanent-error, gcloud-cpp.retry.original-message={"error":"invalid_grant","error_description":"Error connecting to the given credential's issuer."}}}, with a code that isn't equal to OK, but a message that is anything
Step #2: 
Step #2: [  FAILED  ] ExternalAccountImpersonationTest.EAToSAImpersonationRest (152 ms)
Step #2: [ RUN      ] ExternalAccountImpersonationTest.EAToSAImpersonationGrpc
Step #2: WARNING: All log messages before absl::InitializeLog() is called are written to STDERR
Step #2: E0000 00:00:1753797582.907180      38 external_account_credentials.cc:395] Fetch external account credentials access token: UNAVAILABLE: Call to HTTP server ended with status 400 [{"error":"invalid_grant","error_description":"Error connecting to the given credential's issuer."}]
Step #2: E0000 00:00:1753797584.895745      30 external_account_credentials.cc:395] Fetch external account credentials access token: UNAVAILABLE: Call to HTTP server ended with status 400 [{"error":"invalid_grant","error_description":"Error connecting to the given credential's issuer."}]
Step #2: E0000 00:00:1753797587.633246      30 external_account_credentials.cc:395] Fetch external account credentials access token: UNAVAILABLE: Call to HTTP server ended with status 400 [{"error":"invalid_grant","error_description":"Error connecting to the given credential's issuer."}]
Step #2: E0000 00:00:1753797595.205897      27 external_account_credentials.cc:395] Fetch external account credentials access token: UNAVAILABLE: Call to HTTP server ended with status 400 [{"error":"invalid_grant","error_description":"Error connecting to the given credential's issuer."}]
Step #2: E0000 00:00:1753797603.271555      37 external_account_credentials.cc:395] Fetch external account credentials access token: UNAVAILABLE: Call to HTTP server ended with status 400 [{"error":"invalid_grant","error_description":"Error connecting to the given credential's issuer."}]
Step #2: E0000 00:00:1753797625.157134      34 external_account_credentials.cc:395] Fetch external account credentials access token: UNAVAILABLE: Call to HTTP server ended with status 400 [{"error":"invalid_grant","error_description":"Error connecting to the given credential's issuer."}]
Step #2: E0000 00:00:1753797687.287670      34 external_account_credentials.cc:395] Fetch external account credentials access token: UNAVAILABLE: Call to HTTP server ended with status 400 [{"error":"invalid_grant","error_description":"Error connecting to the given credential's issuer."}]
Step #2: E0000 00:00:1753797716.359216      39 external_account_credentials.cc:395] Fetch external account credentials access token: UNAVAILABLE: Call to HTTP server ended with status 400 [{"error":"invalid_grant","error_description":"Error connecting to the given credential's issuer."}]
Step #2: E0000 00:00:1753797774.126996      30 external_account_credentials.cc:395] Fetch external account credentials access token: UNAVAILABLE: Call to HTTP server ended with status 400 [{"error":"invalid_grant","error_description":"Error connecting to the given credential's issuer."}]
Step #2: E0000 00:00:1753798071.531197      28 external_account_credentials.cc:395] Fetch external account credentials access token: UNAVAILABLE: Call to HTTP server ended with status 400 [{"error":"invalid_grant","error_description":"Error connecting to the given credential's issuer."}]
Step #2: E0000 00:00:1753798325.601230      31 external_account_credentials.cc:395] Fetch external account credentials access token: UNAVAILABLE: Call to HTTP server ended with status 400 [{"error":"invalid_grant","error_description":"Error connecting to the given credential's issuer."}]
Step #2: -- Test timed out at 2025-07-29 14:14:39 UTC --

Abre google/cloud/universe_domain/integration_tests/impersonation_tests.cc e inspecciona las pruebas ExternalAccountImpersonationTest.EAToSAImpersonationRest y EAToSAImpersonationGrpc en relación con el fallo reportado. Comprueba cómo se deshabilitan las pruebas de integración y, después, ejecuta el destino de prueba pertinente para confirmar que ambas pruebas que fallan están excluidas y que el resto de la suite de pruebas se ejecuta correctamente.