[release/7.0-staging] [Android] Bump target SDK version for Android sample

[fanyang-mono]

Backport of #80923 to release/7.0-staging

/cc @simonrozsival

This is a test-only change.

Prior to this change, the Android sample app located at src/mono/sample/Android have been failing to install on phones with Android SDK 31+. The error message looks like this

This app was built for an older version of Android and doesn't include the latest privacy protections. 

Installing this app may put your device at risk. Learn more (https://support.google.com/android/answer/2812853?hl=en) about Play Protect.

We use this app to benchmark android app size and startup time. Because of this issue, we weren't able to get data for .NET7 since early November.

This PR added the targetSdkVersion switch and setting it to Android SDK 31. This ensured that the Android app is built for the SDK version aligned with the devices used for testing in the perf lab.

Customer Impact

There is no customer impact. This change is for testing only.

Testing

Validated manually that the Android sample app located at src/mono/sample/Android is able to install on phones with Android SDK 31+ without error.

Risk

None

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Issue Details

---

Backport of #80923 to release/7.0-staging

/cc @simonrozsival

Customer Impact

There is no customer impact. This change is for testing only.

Testing

Validated that the Android sample app located at src/mono/sample/Android is able to install on phones with Android SDK 31+ without error.

Risk

None

Author:	fanyang-mono
Assignees:	-
Labels:	area-Infrastructure-mono
Milestone:	-

[fanyang-mono]

CI failures are unrelated to this PR.

[fanyang-mono]

@carlossanlop This is a test-only change.

[carlossanlop]

@fanyang-mono are the files under src/tasks only used by tests?

src/tasks/AndroidAppBuilder/AndroidAppBuilder.cs

[fanyang-mono]

@fanyang-mono are the files under src/tasks only used by tests?

src/tasks/AndroidAppBuilder/AndroidAppBuilder.cs

yes. We (Mono runtime developers) use it to validate runtime related changes to make sure they works properly with Android apps. .NET Android/MAUI apps doesn't use AndroidAppBuilder to build apps.