Update FlightManagerMockProvider with new methods.

Author: juan-arias

IdentityCore/tests/mocks/MSIDFlightManagerMockProvider.h

@@ -30,6 +30,7 @@ NS_ASSUME_NONNULL_BEGIN
 @interface MSIDFlightManagerMockProvider : NSObject <MSIDFlightManagerInterface>
 
 @property (nonatomic) NSDictionary *boolForKeyContainer;
+@property (nonatomic) NSDictionary *stringForKeyContainer;
 
 @end
 

IdentityCore/tests/mocks/MSIDFlightManagerMockProvider.m

@@ -32,4 +32,10 @@ - (BOOL)boolForKey:(NSString *)flightKey
     return [self.boolForKeyContainer[flightKey] boolValue];
 }
 
+- (nullable NSString *)stringForKey:(nonnull NSString *)flightKey
+{
+    return self.stringForKeyContainer[flightKey];
+}
+
+
 @end