externals: Update fmt to 8.1.1

Merge commit '6633089a44'

externals/fmt/.github/workflows/doc.yml

@@ -12,6 +12,7 @@ jobs:
 
     - name: Create Build Environment
       run: |
+        sudo apt update
         sudo apt install doxygen python3-virtualenv
         sudo npm install -g less clean-css
         cmake -E make_directory ${{runner.workspace}}/build

externals/fmt/.github/workflows/linux.yml

@@ -24,10 +24,11 @@ jobs:
             build_type: Debug
             std: 17
             os: ubuntu-18.04
-          - cxx: g++-10
+          - cxx: g++-11
             build_type: Debug
             std: 20
             os: ubuntu-20.04
+            install: sudo apt install g++-11
           - cxx: clang++-9
             build_type: Debug
             fuzz: -DFMT_FUZZ=ON -DFMT_FUZZ_LINKMAIN=ON