Fix github md "Note" and "Tip" blocks in Android shell README (flutter#50664)

Fixes a couple of misformatted "NOTE" and "TIP" blocks.

[C++, Objective-C, Java style guides]: https://github.com/flutter/engine/blob/main/CONTRIBUTING.md#style

Author: gmackall

shell/platform/android/README.md

@@ -84,7 +84,7 @@ flutter run \
   --local-engine=$ENGINE/out/android_debug_unopt_arm64
 ```
 
-> ![NOTE]
+> [!NOTE]
 > External texture rendering on Android is based on the device API level. For
 > example to test the OpenGLES branch (which uses `SurfaceTexture`), you'll
 > typically need an older device or emulator with an API version 29 or lower.
@@ -105,7 +105,7 @@ See [our wiki](https://github.com/flutter/flutter/wiki/Testing-the-engine#java--
 
 How to edit and contribute to the Android embedder.
 
-> ![TIP]
+> [!TIP]
 > This guide assumes you already have a working Engine development environment:
 >
 > - [Setting up the Engine development environment](https://github.com/flutter/flutter/wiki/Setting-up-the-Engine-development-environment)
@@ -149,7 +149,8 @@ completion:
 
 ![Example](https://github.com/flutter/flutter/assets/168174/8a75dd27-66e1-4c4f-88af-667a73b909b6)
 
-> ![NOTE] > `--compile-commands-dir` must point to an Android build output:
+> [!NOTE]
+> `--compile-commands-dir` must point to an Android build output:
 >
 > ```jsonc
 > {