GithubCI: use Ubuntu 24.04 instead of 23.10

Because 23.10 is no longer supported and 24.04 is LTS release.

After upgrade to Ubuntu 24.04 dotnet6 is no longer available in
main .deb repository. So we have to use dotnet-sdk-8.0.

To be able to run .NET6 tools using .NET8, set
DOTNET_ROLL_FORWARD env. var to Major.

Build conventions.sln before lint to get rid of error:
```
Lint failed to parse files. Failed with: Type check failed. You might want to build your solution/project first and try again.
```

.github/workflows/CI.yml

@@ -9,13 +9,16 @@ on:
   schedule:
     - cron: "0 0 * * *"
 
+# As we use .NET 8 now, to run tools compiled for .NET 6 we need to set roll-forward to major
+env:
+  DOTNET_ROLL_FORWARD: Major
+
 jobs:
   build-fs:
     name: Build F#
-    # TODO: upgrade to 24.04->24.04 (because LTS) as soon as it's available, instead of 22.04->23.10
-    runs-on: ubuntu-22.04
+    runs-on: ubuntu-24.04
     container:
-      image: "ubuntu:23.10"
+      image: "ubuntu:24.04"
     steps:
       - uses: actions/checkout@v4
       - name: Install required dependencies
@@ -32,7 +35,7 @@ jobs:
           # The remote certificate is invalid because of errors in the certificate chain: UntrustedRoot
           apt install --yes --no-install-recommends ca-certificates
 
-          apt install --yes --no-install-recommends dotnet6
+          apt install --yes --no-install-recommends dotnet-sdk-8.0
 
       - name: Compile the conventions solution
         run: dotnet build --configuration Release conventions.sln
@@ -42,10 +45,9 @@ jobs:
   file-conventions-tests:
     name: Run FileConventions-lib unit tests
     needs: build-fs
-    # TODO: upgrade to 24.04->24.04 (because LTS) as soon as it's available, instead of 22.04->23.10
-    runs-on: ubuntu-22.04
+    runs-on: ubuntu-24.04
     container:
-      image: "ubuntu:23.10"
+      image: "ubuntu:24.04"
     steps:
       - uses: actions/checkout@v4
       - name: Install required dependencies
@@ -61,18 +63,17 @@ jobs:
           # The remote certificate is invalid because of errors in the certificate chain: UntrustedRoot
           apt install --yes --no-install-recommends ca-certificates
 
-          apt install --yes --no-install-recommends dotnet6
+          apt install --yes --no-install-recommends dotnet-sdk-8.0
 
       - name: Run tests to validate F# scripts
         run: dotnet test src/FileConventions.Test/FileConventions.Test.fsproj
 
   build-ts:
     name: Build TypeScript
 
-    # TODO: upgrade to 24.04->24.04 (because LTS) as soon as it's available, instead of 22.04->23.10
-    runs-on: ubuntu-22.04
+    runs-on: ubuntu-24.04
     container:
-      image: "ubuntu:23.10"
+      image: "ubuntu:24.04"
     steps:
       - uses: actions/checkout@v4
       - name: Install required dependencies
@@ -106,10 +107,9 @@ jobs:
   commitlint-plugins-tests:
     name: Run commitlint-related tests
     needs: build-ts
-    # TODO: upgrade to 24.04->24.04 (because LTS) as soon as it's available, instead of 22.04->23.10
-    runs-on: ubuntu-22.04
+    runs-on: ubuntu-24.04
     container:
-      image: "ubuntu:23.10"
+      image: "ubuntu:24.04"
     steps:
       - uses: actions/checkout@v4
       - name: Install required dependencies
@@ -149,10 +149,9 @@ jobs:
     needs:
       - file-conventions-tests
       - commitlint-plugins-tests
-    # TODO: upgrade to 24.04->24.04 (because LTS) as soon as it's available, instead of 22.04->23.10
-    runs-on: ubuntu-22.04
+    runs-on: ubuntu-24.04
     container:
-      image: "ubuntu:23.10"
+      image: "ubuntu:24.04"
     env:
       GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
     steps:
@@ -193,7 +192,7 @@ jobs:
           # The remote certificate is invalid because of errors in the certificate chain: UntrustedRoot
           apt install --yes --no-install-recommends ca-certificates
 
-          apt install --yes --no-install-recommends dotnet6
+          apt install --yes --no-install-recommends dotnet-sdk-8.0
 
       - name: Check all files end with EOL
         run: dotnet fsi scripts/eofConvention.fsx
@@ -245,6 +244,7 @@ jobs:
         run: |
           dotnet new tool-manifest
           dotnet tool install dotnet-fsharplint --version 0.23.7--date20240109-1215.git-a263185
+          dotnet build conventions.sln
           dotnet dotnet-fsharplint lint conventions.sln
       - name: fantomless
         run: |