[Release] Update library version to 1.13.0-alpha08

PiperOrigin-RevId: 698824267

build.gradle

@@ -59,7 +59,7 @@ ext {
     ? project.property('mavenRepoUrl') : '/tmp/myRepo/')
 
   // Current version of the library (could be in-development/unreleased).
-  mdcLibraryVersion = '1.13.0-alpha07'
+  mdcLibraryVersion = '1.13.0-alpha08'
   mdcLibraryPackage = "com.google.android.material"
   mdcLibraryDir = "com/google/android/material"
 }