test(xds): relax getHandshakeSession mock verification in XdsX509TrustManagerTest (#12861) (#12966)

In JDK 28, `X509TrustManagerImpl` retrieves the handshake session
multiple times during certificate verification. PR #12861 relaxed one
verification to `atLeastOnce()`, but left `times(1)` on the remaining
five test cases in `XdsX509TrustManagerTest`.

This change relaxes all remaining `getHandshakeSession()` mock
verifications in `XdsX509TrustManagerTest` from `times(1)` to
`atLeastOnce()`.

Author: AgraVator

xds/src/test/java/io/grpc/xds/internal/security/trust/XdsX509TrustManagerTest.java

@@ -569,7 +569,7 @@ public void checkServerTrustedSslEngineSpiffeTrustMap()
     trustManager = XdsTrustManagerFactory.createX509TrustManager(
         ImmutableMap.of("example.com", caCerts), null, false);
     trustManager.checkServerTrusted(serverCerts, "ECDHE_ECDSA", sslEngine);
-    verify(sslEngine, times(1)).getHandshakeSession();
+    verify(sslEngine, atLeastOnce()).getHandshakeSession();
     assertThat(sslEngine.getSSLParameters().getEndpointIdentificationAlgorithm()).isEmpty();
   }
 
@@ -636,7 +636,7 @@ public void checkServerTrustedSslEngine_untrustedServer_expectException()
       assertThat(expected).hasMessageThat()
           .endsWith("unable to find valid certification path to requested target");
     }
-    verify(sslEngine, times(1)).getHandshakeSession();
+    verify(sslEngine, atLeastOnce()).getHandshakeSession();
   }
 
   @Test
@@ -647,7 +647,7 @@ public void checkServerTrustedSslSocket()
         CertificateUtils.toX509Certificates(TlsTesting.loadCert(SERVER_1_PEM_FILE));
     trustManager.checkServerTrusted(serverCerts, "ECDHE_ECDSA", sslSocket);
     verify(sslSocket, times(1)).isConnected();
-    verify(sslSocket, times(1)).getHandshakeSession();
+    verify(sslSocket, atLeastOnce()).getHandshakeSession();
     assertThat(sslSocket.getSSLParameters().getEndpointIdentificationAlgorithm()).isEmpty();
   }
 
@@ -663,7 +663,7 @@ public void checkServerTrustedSslSocketSpiffeTrustMap()
         ImmutableMap.of("example.com", caCerts), null, false);
     trustManager.checkServerTrusted(serverCerts, "ECDHE_ECDSA", sslSocket);
     verify(sslSocket, times(1)).isConnected();
-    verify(sslSocket, times(1)).getHandshakeSession();
+    verify(sslSocket, atLeastOnce()).getHandshakeSession();
     assertThat(sslSocket.getSSLParameters().getEndpointIdentificationAlgorithm()).isEmpty();
   }
 
@@ -681,7 +681,7 @@ public void checkServerTrustedSslSocket_untrustedServer_expectException()
           .endsWith("unable to find valid certification path to requested target");
     }
     verify(sslSocket, times(1)).isConnected();
-    verify(sslSocket, times(1)).getHandshakeSession();
+    verify(sslSocket, atLeastOnce()).getHandshakeSession();
   }
 
   @Test