Use alpha 7 of media2-widget

Alpha is removed and replaced by alpha 7.

Test: Re-sync AS project
Change-Id: I1a523cf1d5fbedb511ac0a63f46bb14420ace21d
diff --git a/build.gradle b/build.gradle
index 6949d04..7393c50 100644
--- a/build.gradle
+++ b/build.gradle
@@ -64,7 +64,7 @@
 dependencies {
     implementation 'androidx.appcompat:appcompat:1.0.2'
     implementation 'androidx.constraintlayout:constraintlayout:2.0.0-alpha3'
-    implementation 'androidx.media2:media2-widget:1.0.0-alpha06'
+    implementation 'androidx.media2:media2-widget:1.0.0-alpha07'
     implementation 'androidx.mediarouter:mediarouter:1.0.0'
     implementation 'com.google.android.material:material:1.0.0'
 }