Use C++20. (#2322)

.github/workflows/CI.yml

@@ -280,7 +280,7 @@ jobs:
         include:  # package these differently
           - type: AppImage
             EXTRA_ARGS: '-DSUNSHINE_BUILD_APPIMAGE=ON'
-            dist: 20.04
+            dist: 22.04
 
     steps:
       - name: Maximize build space
@@ -323,6 +323,9 @@ jobs:
           # allow newer gcc
           sudo add-apt-repository ppa:ubuntu-toolchain-r/test -y
 
+          # allow libfuse2 for appimage on 22.04
+          sudo add-apt-repository universe
+
           sudo apt-get install -y \
             build-essential \
             cmake \
@@ -338,6 +341,7 @@ jobs:
             libcurl4-openssl-dev \
             libdrm-dev \
             libevdev-dev \
+            libfuse2 \
             libminiupnpc-dev \
             libmfx-dev \
             libnotify-dev \