Add missing <TargetConditionals.h> before TARGET_OS_OSX test (#6186)

Author: paulb777

FirebaseInstallations/Source/Tests/Integration/FIRInstallationsIntegrationTests.m

@@ -20,6 +20,8 @@
 // macOS requests a user password when accessing the Keychain for the first time,
 // so the tests may fail. Disable integration tests on macOS so far.
 // TODO: Configure the tests to run on macOS without requesting the keychain password.
+
+#import <TargetConditionals.h>
 #if !TARGET_OS_OSX
 
 #import <XCTest/XCTest.h>

FirebaseInstallations/Source/Tests/Utils/FIRTestKeychain.m

@@ -14,6 +14,7 @@
  * limitations under the License.
  */
 
+#import <TargetConditionals.h>
 #if TARGET_OS_OSX
 
 #import "FirebaseInstallations/Source/Tests/Utils/FIRTestKeychain.h"

GoogleUtilities/Tests/Unit/Utils/GULTestKeychain.m

@@ -14,6 +14,7 @@
  * limitations under the License.
  */
 
+#import <TargetConditionals.h>
 #if TARGET_OS_OSX
 
 #import "GoogleUtilities/Tests/Unit/Utils/GULTestKeychain.h"