Use ppa to update libfmt from 4.x (ubuntu 18.04)

.github/workflows/stable-compilation.yml

@@ -32,6 +32,12 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v2
 
+      - name: Install ppa for new libfmt
+        if: matrix.image == 'ubuntu:18.04'
+        run: |
+          echo "deb http://ppa.launchpad.net/team-xbmc/ppa/ubuntu bionic main" | tee -a /etc/apt/sources.list
+          apt-key adv --keyserver keyserver.ubuntu.com --recv 0x189701DA570C56B9488EF60A6D975C4791E7EE5E
+
       - name: Install dependencies
         run: |
           export DEBIAN_FRONTEND="noninteractive"
@@ -41,7 +47,7 @@ jobs:
             libicu-dev libexpat1-dev libsdl2-dev libpng-dev libpixman-1-dev \
             libfmt-dev libfreetype6-dev libharfbuzz-dev libmpg123-dev \
             libsndfile-dev libvorbis-dev libopusfile-dev libspeexdsp-dev \
-            libdrm-dev libgbm-dev # only needed for 21.04
+            libdrm-dev libgbm-dev # only needed for sdl2 on ubuntu 21.04
 
       - name: Compile
         run: |