ci: try to build with cpp_std=c++20

Add an extra job to build with `-std=c++20` on Fedora.
Update actions/checkout to v3.

.github/workflows/freebsd.yml

@@ -9,7 +9,7 @@ jobs:
     # https://github.com/actions/virtual-environments/issues/4060 - for lack of VirtualBox on MacOS 11 runners
     runs-on: macos-12
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v3
     - name: Test in FreeBSD VM
       uses: vmactions/freebsd-vm@v0
       with:

.github/workflows/lint.yml

@@ -6,7 +6,7 @@ jobs:
   build:
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v3
     - uses: DoozyX/clang-format-lint-action@v0.13
       with:
         source: '.'

.github/workflows/linux.yml

@@ -13,16 +13,20 @@ jobs:
           - fedora
           - opensuse
           - gentoo
+        cpp_std: [c++17]
+        include:
+          - distro: fedora
+            cpp_std: c++20
 
     runs-on: ubuntu-latest
     container:
       image: alexays/waybar:${{ matrix.distro }}
 
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
       - name: configure
-        run: meson -Dman-pages=enabled build
+        run: meson -Dman-pages=enabled -Dcpp_std=${{matrix.cpp_std}} build
       - name: build
         run: ninja -C build
       - name: test
-        run: meson test -C build --no-rebuild --print-errorlogs --suite waybar
+        run: meson test -C build --no-rebuild --verbose --suite waybar