Centralize IrrlichtMt version used for builds

maybe a submodule would have really been easier...

.github/workflows/build.yml

@@ -226,11 +226,9 @@ jobs:
       - uses: actions/checkout@v3
 
       - name: Checkout IrrlichtMt
-        uses: actions/checkout@v3
-        with:
-          repository: minetest/irrlicht
-          path: lib/irrlichtmt/
-          ref: "1.9.0mt7"
+        run: |
+          $ref = @(Get-Content misc\irrlichtmt_tag.txt)
+          git clone https://github.com/minetest/irrlicht lib\irrlichtmt --depth 1 -b $ref[0]
 
       - name: Restore from cache and run vcpkg
         uses: lukka/run-vcpkg@v7

.github/workflows/macos.yml

@@ -22,7 +22,6 @@ on:
       - '.github/workflows/macos.yml'
 
 env:
-  IRRLICHT_TAG: 1.9.0mt7
   MINETEST_GAME_REPO: https://github.com/minetest/minetest_game.git
   MINETEST_GAME_BRANCH: master
   MINETEST_GAME_NAME: minetest_game
@@ -43,8 +42,7 @@ jobs:
       - name: Build
         run: |
           git clone -b $MINETEST_GAME_BRANCH $MINETEST_GAME_REPO games/$MINETEST_GAME_NAME
-          rm -rvf games/$MINETEST_GAME_NAME/.git
-          git clone https://github.com/minetest/irrlicht -b $IRRLICHT_TAG lib/irrlichtmt
+          git clone https://github.com/minetest/irrlicht lib/irrlichtmt --depth 1 -b $(cat misc/irrlichtmt_tag.txt)
           mkdir build
           cd build
           cmake .. \