GDTCORClockTest: decrease expected timestamp accuracy to fix test flakes (#6330)

Author: maksymmalyhin

GoogleDataTransport/GDTCORTests/Unit/GDTCORClockTest.m

@@ -90,7 +90,7 @@ - (void)testUptime {
   XCTAssertGreaterThan(clock2.uptimeNanoseconds, clock1.uptimeNanoseconds);
   NSTimeInterval uptimeDiff =
       (clock2.uptimeNanoseconds - clock1.uptimeNanoseconds) / (double)NSEC_PER_SEC;
-  NSTimeInterval accuracy = 0.1;
+  NSTimeInterval accuracy = 0.2;
 
   // Assert that uptime difference reflects the actually passed time.
   XCTAssertLessThanOrEqual(ABS(uptimeDiff - timeDiff), accuracy);
@@ -107,7 +107,7 @@ - (void)testUptimeMilliseconds {
   NSTimeInterval millisecondsPerSecond = 1000;
   NSTimeInterval uptimeDiff =
       ([clock2 uptimeMilliseconds] - [clock1 uptimeMilliseconds]) / millisecondsPerSecond;
-  NSTimeInterval accuracy = 0.1;
+  NSTimeInterval accuracy = 0.2;
 
   // Assert that uptime difference reflects the actually passed time.
   XCTAssertLessThanOrEqual(ABS(uptimeDiff - timeDiff), accuracy);