Added UPM branch workflow.

Author: Uralstech

.github/workflows/upm-subtree-split.yml

@@ -0,0 +1,18 @@
+# Taken from https://github.com/RageAgainstThePixel/upm-subtree-split
+
+name: upm-subtree-split
+
+on:
+  push:
+    branches:
+    - main
+
+jobs:
+  upm-subtree-split:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v4
+      with:
+        fetch-depth: 0
+
+    - uses: RageAgainstThePixel/upm-subtree-split@v1.1