Rename to Luanti (#15294)

The new header intentionally isn't in MTG stone design (or any other MTG-esque design), since we want to distance Luanti and MTG from each other. The font "undefined medium" (https://undefined-medium.com/) was used. 

ASCII art generated by https://patorjk.com/software/taag/#p=display&f=Graffiti&t=luanti
https://github.com/minetest/minetest/pull/11952#issuecomment-1013364703

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Co-authored-by: sfan5 <sfan5@live.de>

.github/workflows/android.yml

@@ -50,25 +50,25 @@ jobs:
     - name: Save AAB artifact
       uses: actions/upload-artifact@v4
       with:
-        name: Minetest-release.aab
+        name: Luanti-release.aab
         path: android/app/build/outputs/bundle/release/app-release.aab
     - name: Save armeabi artifact
       uses: actions/upload-artifact@v4
       with:
-        name: Minetest-armeabi-v7a.apk
+        name: Luanti-armeabi-v7a.apk
         path: android/app/build/outputs/apk/release/app-armeabi-v7a-release-unsigned.apk
     - name: Save arm64 artifact
       uses: actions/upload-artifact@v4
       with:
-        name: Minetest-arm64-v8a.apk
+        name: Luanti-arm64-v8a.apk
         path: android/app/build/outputs/apk/release/app-arm64-v8a-release-unsigned.apk
     - name: Save x86 artifact
       uses: actions/upload-artifact@v4
       with:
-        name: Minetest-x86.apk
+        name: Luanti-x86.apk
         path: android/app/build/outputs/apk/release/app-x86-release-unsigned.apk
     - name: Save x86_64 artifact
       uses: actions/upload-artifact@v4
       with:
-        name: Minetest-x86_64.apk
+        name: Luanti-x86_64.apk
         path: android/app/build/outputs/apk/release/app-x86_64-release-unsigned.apk