Update CMake version for AV1 extension

The specified CMake version doesn't work with the latest
Android Studio releases. Updating to a more recent version
fixes the problem.

Issue: google/ExoPlayer#9933
PiperOrigin-RevId: 467634063
(cherry picked from commit 80b635e7)

extensions/av1/build.gradle

@@ -32,7 +32,7 @@ android {
 if (project.file('src/main/jni/libgav1').exists()) {
     android.externalNativeBuild.cmake {
         path = 'src/main/jni/CMakeLists.txt'
-        version = '3.7.1+'
+        version = '3.21.0+'
         if (project.hasProperty('externalNativeBuildDir')) {
             if (!new File(externalNativeBuildDir).isAbsolute()) {
                 ext.externalNativeBuildDir =

extensions/av1/src/main/jni/CMakeLists.txt

@@ -14,7 +14,8 @@
 # limitations under the License.
 #
 
-cmake_minimum_required(VERSION 3.7.1 FATAL_ERROR)
+cmake_minimum_required(VERSION 3.21.0 FATAL_ERROR)
+
 set(CMAKE_CXX_STANDARD 11)
 
 project(libgav1JNI C CXX)