test: add missing testIDs for maestro selectors

Add signMessageInput and signMessageButton testIDs to the Sign Message
scene so UI automation can drive the message field and sign action by a
stable selector.

Author: j0ntz

src/components/scenes/SignMessageScene.tsx

@@ -112,6 +112,7 @@ const SignMessageSceneComponent: React.FC<Props> = props => {
           multiline
           numberOfLines={4}
           placeholder={lstrings.sign_message_input_placeholder}
+          testID="signMessageInput"
           value={message}
           onChangeText={handleChangeMessage}
         />
@@ -135,7 +136,8 @@ const SignMessageSceneComponent: React.FC<Props> = props => {
             label: lstrings.sign_message_sign_button,
             onPress: handleSign,
             disabled: message === '' || publicAddress == null,
-            spinner: isSigning
+            spinner: isSigning,
+            testID: 'signMessageButton'
           }}
         />
       </View>