Use custom sources for GH Actions build on Ubuntu

.github/workflows/build_linux.yml

@@ -8,18 +8,18 @@ jobs:
     name: Editor (Linux, Development x64)
     runs-on: "ubuntu-20.04"
     steps:
-    - name: Install dependencies
-      run: |
-        sudo rm -f /etc/apt/sources.list.d/*
-        sudo cp -f Development/Scripts/Linux/build_linux_sources.list /etc/apt/sources.list
-        sudo apt-get update
-        sudo apt-get install libx11-dev libxcursor-dev libxinerama-dev build-essential gettext libtool libtool-bin libpulse-dev libasound2-dev libjack-dev portaudio19-dev
     - name: Checkout repo
       uses: actions/checkout@v2
     - name: Checkout LFS
       run: |
         git lfs version
         git lfs pull
+    - name: Install dependencies
+      run: |
+        sudo rm -f /etc/apt/sources.list.d/*
+        sudo cp -f .github/workflows/build_linux_sources.list /etc/apt/sources.list
+        sudo apt-get update
+        sudo apt-get install libx11-dev libxcursor-dev libxinerama-dev build-essential gettext libtool libtool-bin libpulse-dev libasound2-dev libjack-dev portaudio19-dev
     - name: Build
       run: |
         ./Development/Scripts/Linux/CallBuildTool.sh -build -log -arch=x64 -platform=Linux -configuration=Development -buildtargets=FlaxEditor