Remove NET 6.0 from GitHub Actions (#5083)

Author: lahma

Diff for: .github/workflows/build.yml

@@ -43,7 +43,7 @@ jobs:
       - uses: actions/setup-dotnet@v4
         with:
           dotnet-version: |
-            6.0
+            8.0
             9.0
       - uses: actions/checkout@v4
       - name: 'Run: Compile, Test, Pack, Publish'
@@ -80,7 +80,7 @@ jobs:
       - uses: actions/setup-dotnet@v4
         with:
           dotnet-version: |
-            6.0
+            8.0
             9.0
       - uses: actions/checkout@v4
       - name: 'Run: Compile, Test, Pack, Publish'
@@ -97,7 +97,7 @@ jobs:
       - uses: actions/setup-dotnet@v4
         with:
           dotnet-version: |
-            6.0
+            8.0
             9.0
       - uses: actions/checkout@v4
       - name: 'Run: Compile, Test, Pack, Publish'

Diff for: .github/workflows/pr.yml

@@ -45,7 +45,7 @@ jobs:
       - uses: actions/setup-dotnet@v4
         with:
           dotnet-version: |
-            6.0
+            8.0
             9.0
       - uses: actions/checkout@v4
       - name: 'Run: Compile, Test, Pack'
@@ -77,7 +77,7 @@ jobs:
       - uses: actions/setup-dotnet@v4
         with:
           dotnet-version: |
-            6.0
+            8.0
             9.0
       - uses: actions/checkout@v4
       - name: 'Run: Compile, Test, Pack'
@@ -89,7 +89,7 @@ jobs:
       - uses: actions/setup-dotnet@v4
         with:
           dotnet-version: |
-            6.0
+            8.0
             9.0
       - uses: actions/checkout@v4
       - name: 'Run: Compile, Test, Pack'

Diff for: build/Build.CI.GitHubActions.cs

@@ -46,8 +46,7 @@ protected override GitHubActionsJob GetJobs(GitHubActionsImage image, IReadOnlyC
 
         var newSteps = new List<GitHubActionsStep>(job.Steps);
 
-        // only need to list the ones that are missing from default image
-        newSteps.Insert(0, new GitHubActionsSetupDotNetStep(["6.0", "9.0"]));
+        newSteps.Insert(0, new GitHubActionsSetupDotNetStep(["8.0", "9.0"]));
 
         var onWindows = image.ToString().StartsWith("windows", StringComparison.OrdinalIgnoreCase);
         if (onWindows)