Fix import in `GenerateContentResponseTests.swift`

FirebaseAI/Tests/Unit/Types/GenerateContentResponseTests.swift

@@ -12,7 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-import FirebaseVertexAI
+import FirebaseAI
 import XCTest
 
 @available(iOS 15.0, macOS 12.0, macCatalyst 15.0, tvOS 15.0, watchOS 8.0, *)