[camera_android_camerax] Update Android minimum SDK version (#9945)

#9853 bumped it to 23, so updating the README.

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Author: camsim99

packages/camera/camera/README.md

@@ -8,7 +8,7 @@ A Flutter plugin for iOS, Android and Web allowing access to the device cameras.
 
 |                | Android | iOS       | Web                    |
 |----------------|---------|-----------|------------------------|
-| **Support**    | SDK 21+ | iOS 12.0+ | [See `camera_web `][1] |
+| **Support**    | SDK 23+ | iOS 12.0+ | [See `camera_web `][1] |
 
 ## Features
 
@@ -37,10 +37,10 @@ If editing `Info.plist` as text, add:
 
 ### Android
 
-Change the minimum Android sdk version to 21 (or higher) in your `android/app/build.gradle` file.
+Change the minimum Android sdk version to 23 (or higher) in your `android/app/build.gradle` file.
 
 ```groovy
-minSdkVersion 21
+minSdk = 23
 ```
 
 The endorsed [`camera_android_camerax`][2] implementation of the camera plugin built with CameraX has