Fix Fireperf flaky tests (#8818)

Author: jeremyjiang-dev

FirebasePerformance/Tests/Unit/FPRNetworkTraceTest.m

@@ -125,6 +125,7 @@ - (void)testTraceCreationWhenSDKFlagDisabled {
 
   // Trigger the RC config fetch
   remoteConfig.lastFetchTime = nil;
+  configFlags.appStartConfigFetchDelayInSeconds = 0.0;
   [configFlags update];
 
   XCTAssertNil([[FPRNetworkTrace alloc] initWithURLRequest:self.testURLRequest]);

FirebasePerformance/Tests/Unit/Gauges/FPRGaugeManagerTests.m

@@ -75,6 +75,7 @@ - (void)testGaugeCollectionEnabledWhenSDKFlagEnabled {
 
   // Trigger the RC config fetch
   remoteConfig.lastFetchTime = nil;
+  configFlags.appStartConfigFetchDelayInSeconds = 0.0;
   [configFlags update];
 
   [FPRGaugeManager sharedInstance].isColdStart = NO;

FirebasePerformance/Tests/Unit/Instruments/FIRHTTPMetricTests.m

@@ -103,6 +103,7 @@ - (void)testMetricCreationWhenSDKFlagDisabled {
 
   // Trigger the RC config fetch
   remoteConfig.lastFetchTime = nil;
+  configFlags.appStartConfigFetchDelayInSeconds = 0.0;
   [configFlags update];
 
   XCTAssertNil([[FIRHTTPMetric alloc] initWithURL:self.sampleURL HTTPMethod:FIRHTTPMethodGET]);

FirebasePerformance/Tests/Unit/Timer/FIRTraceTest.m

@@ -83,6 +83,7 @@ - (void)testTraceCreationWhenSDKFlagDisabled {
 
   // Trigger the RC config fetch
   remoteConfig.lastFetchTime = nil;
+  configFlags.appStartConfigFetchDelayInSeconds = 0.0;
   [configFlags update];
 
   XCTAssertNil([[FIRTrace alloc] initWithName:@"Random"]);