General: Bump CI actions off the deprecated Node 20 runtime (#34)

GitHub is deprecating the Node 20 runtime and already force-runs these
two actions on Node 24, emitting a warning on every job that uses the
common-setup composite.

- android-actions/setup-android v3.2.2 -> v4.0.1 (v4.0.0 was the Node 24
  migration). Inputs are unchanged and we pass none; the only behavioral
  change is the default cmdline-tools version moving 11076708 -> 14742923
  (20.0), which matches what recent AGP/compileSdk needs anyway.
- gradle/actions/wrapper-validation v4.4.4 -> v6.2.0 (Node 24 since v5).
  Inputs are unchanged and we pass none. v6 split caching into the
  proprietary gradle-actions-caching component, but wrapper-validation is
  part of the MIT action runner and its dist bundle never loads it; this
  repo caches via actions/setup-java's `cache: gradle`, not setup-gradle.

No other action in the repo targets Node 20. Verified against the same
job before and after: the warning annotation is present on the last main
run and absent on this one.

Author: d4rken

.github/actions/common-setup/action.yml

@@ -13,7 +13,7 @@ runs:
         cache: gradle
 
     - name: Set up Android SDK
-      uses: android-actions/setup-android@9fc6c4e9069bf8d3d10b2204b1fb8f6ef7065407 #v3.2.2
+      uses: android-actions/setup-android@40fd30fb8d7440372e1316f5d1809ec01dcd3699 #v4.0.1
 
     - name: Validate Gradle wrapper
-      uses: gradle/actions/wrapper-validation@748248ddd2a24f49513d8f472f81c3a07d4d50e1 #v4.4.4
+      uses: gradle/actions/wrapper-validation@3f131e8634966bd73d06cc69884922b02e6faf92 #v6.2.0