Increase test timeouts to reduce flakiness.

src/objective-c/tests/GRPCClientTests.m

@@ -114,7 +114,7 @@ static ProtoMethod *kUnaryCallMethod;
 
   [call startWithWriteable:responsesWriteable];
 
-  [self waitForExpectationsWithTimeout:4 handler:nil];
+  [self waitForExpectationsWithTimeout:8 handler:nil];
 }
 
 - (void)testSimpleProtoRPC {
@@ -146,7 +146,7 @@ static ProtoMethod *kUnaryCallMethod;
 
   [call startWithWriteable:responsesWriteable];
 
-  [self waitForExpectationsWithTimeout:4 handler:nil];
+  [self waitForExpectationsWithTimeout:8 handler:nil];
 }
 
 - (void)testMetadata {

src/objective-c/tests/InteropTests.m

@@ -128,7 +128,7 @@ static NSString * const kRemoteSSLHost = @"grpc-test.sandbox.google.com";
     [expectation fulfill];
   }];
 
-  [self waitForExpectationsWithTimeout:8 handler:nil];
+  [self waitForExpectationsWithTimeout:16 handler:nil];
 }
 
 - (void)testClientStreamingRPC {