Use PendingIntent.FLAG_IMMUTABLE flag for our intents

[luk1337]

AniTrend Pull Request

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Description

This is required since we target Android 12+ API:
https://developer.android.com/guide/components/intents-filters#DeclareMutabilityPendingIntent

Motivation and Context

See #489

How Has This Been Tested?

Compile tested.

Screenshots (if appropriate):

n/a

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

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[wax911]

Thanks @luk1337 💯