GitHubCI,Frontend.Console: swap .net6 with .net8

This is to fix this compiler error when building in Release
mode:

```
Determining projects to restore...
/usr/share/dotnet/sdk/10.0.100/Sdks/Microsoft.NET.Sdk/targets/Microsoft.NET.EolTargetFrameworks.targets(32,5): error NETSDK1138: The target framework 'net6.0' is out of support and will not receive security updates in the future. Please refer to https://aka.ms/dotnet-core-support for more information about the support policy. [/home/runner/work/geewallet/geewallet/src/GWallet.Frontend.Console/GWallet.Frontend.Console.fsproj]
```

Author: knocte

.github/workflows/CI.yml

@@ -9,23 +9,25 @@ on:
   schedule:
     - cron: "0 0 * * *"
 
+env:
+  DOTNET_VERSION: '8.0.22'
 
 # FIXME: figure out why we need to clean after make if we
 # want 'make strict' target to really happen without
 # assuming the binaries from previous build are good
 # (msbuild bug?)
 
 jobs:
-  macOS--dotnet6-and-mono:
+  macOS--dotnet-and-mono:
     runs-on: macOS-13
     steps:
     - uses: actions/checkout@v1
       with:
         submodules: false
-    - name: Setup .NET SDK 6.0.x
+    - name: Setup .NET SDK
       uses: actions/[email protected]
       with:
-        dotnet-version: '6.0.113'
+        dotnet-version: ${{ env.DOTNET_VERSION }}
     - name: Install specific Xamarin.iOS and Xamarin.Android versions
       run: |
         wget https://download.visualstudio.microsoft.com/download/pr/81c41aaa-a3d7-4875-8416-d04b472379b7/21d9f6c5ad3a6bc2479b2ec4b0685b6c/xamarin.ios-16.0.0.72.pkg
@@ -94,16 +96,16 @@ jobs:
     - name: integration tests
       run: make update-servers
 
-  macOS--dotnet6-only:
+  macOS--dotnet-only:
     runs-on: macOS-13
     steps:
     - uses: actions/checkout@v1
       with:
         submodules: false
-    - name: Setup .NET SDK 6.0.x
+    - name: Setup .NET SDK
       uses: actions/[email protected]
       with:
-        dotnet-version: '6.0.113'        
+        dotnet-version: ${{ env.DOTNET_VERSION }}        
     - name: HACK to emulate mono uninstall
       run: sudo rm -f `which mono` && sudo rm -f `which msbuild`
     - name: configure
@@ -121,16 +123,16 @@ jobs:
     - name: integration tests
       run: make update-servers
 
-  windows--dotnet6-and-legacyFramework:
+  windows--dotnet-and-legacyFramework:
     runs-on: windows-latest
     steps:
     - uses: actions/checkout@v1
       with:
         submodules: false
-    - name: Setup .NET SDK 6.0.x
+    - name: Setup .NET SDK
       uses: actions/[email protected]
       with:
-        dotnet-version: '6.0.113'
+        dotnet-version: ${{ env.DOTNET_VERSION }}
     - name: configure
       run: .\configure.bat
     - name: build in DEBUG mode
@@ -178,16 +180,16 @@ jobs:
     - name: integration tests
       run: .\make update-servers
 
-  windows--dotnet6-only:
+  windows--dotnet-only:
     runs-on: windows-latest
     steps:
     - uses: actions/checkout@v1
       with:
         submodules: false
-    - name: Setup .NET SDK 6.0.x
+    - name: Setup .NET SDK
       uses: actions/[email protected]
       with:
-        dotnet-version: '6.0.113'
+        dotnet-version: ${{ env.DOTNET_VERSION }}
     - name: HACK to emulate legacy .NETFramework uninstall
       run: del $(& "${Env:ProgramFiles(x86)}\Microsoft Visual Studio\Installer\vswhere.exe" -find MSBuild\\**\\Bin\\MSBuild.exe)
     - name: configure

src/GWallet.Frontend.Console/GWallet.Frontend.Console.fsproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <TargetFramework>net6.0</TargetFramework>
+    <TargetFramework>net8.0</TargetFramework>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="..\GWallet.Backend\Properties\CommonAssemblyInfo.fs">