[webview]: Bump gradle

Bumps gradle from 3.3.0 to 7.2.1.

---
updated-dependencies:
- dependency-name: com.android.tools.build:gradle
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

packages/webview_flutter/webview_flutter_android/example/android/build.gradle

@@ -5,7 +5,7 @@ buildscript {
     }
 
     dependencies {
-        classpath 'com.android.tools.build:gradle:3.3.0'
+        classpath 'com.android.tools.build:gradle:7.2.1'
     }
 }