only handle tags, ignore pull request behavior

Author: david-driscoll

src/GitVersion.BuildAgents.Tests/Agents/GitHubActionsTests.cs

@@ -90,16 +90,13 @@ public void GetCurrentBranchShouldHandleTags()
     public void GetCurrentBranchShouldHandlePullRequests()
     {
         // Arrange
-        this.environment.SetEnvironmentVariable("GITHUB_EVENT_NAME", "pull_request");
-        this.environment.SetEnvironmentVariable("GITHUB_HEAD_REF", "some-branch");
-        this.environment.SetEnvironmentVariable("GITHUB_BASE_REF", MainBranch);
         this.environment.SetEnvironmentVariable("GITHUB_REF", "refs/pull/1/merge");
 
         // Act
         var result = this.buildServer.GetCurrentBranch(false);
 
         // Assert
-        result.ShouldBe("some-branch");
+        result.ShouldBe("refs/pull/1/merge");
     }
 
     [Test]

src/GitVersion.BuildAgents/Agents/GitHubActions.cs

@@ -53,24 +53,12 @@ public override void WriteIntegration(Action<string?> writer, GitVersionVariable
 
     public override string? GetCurrentBranch(bool usingDynamicRepos)
     {
-        var refType = Environment.GetEnvironmentVariable("GITHUB_REF_TYPE") ?? "";
-        var eventName = Environment.GetEnvironmentVariable("GITHUB_EVENT_NAME") ?? "";
         // https://docs.github.com/en/actions/learn-github-actions/environment-variables#default-environment-variables
         // GITHUB_REF must be used only for "real" branches, not for tags.
         // Bug fix for https://github.com/GitTools/GitVersion/issues/2838
 
-        // pull_request or pull_request_target
-        if (eventName.StartsWith("pull_request", StringComparison.OrdinalIgnoreCase))
-        {
-            return Environment.GetEnvironmentVariable("GITHUB_HEAD_REF");
-        }
-
-        if (refType.Equals("tag", StringComparison.OrdinalIgnoreCase))
-        {
-            return null;
-        }
-
-        return Environment.GetEnvironmentVariable("GITHUB_REF");
+        var refType = Environment.GetEnvironmentVariable("GITHUB_REF_TYPE") ?? "";
+        return refType.Equals("tag", StringComparison.OrdinalIgnoreCase) ? null : Environment.GetEnvironmentVariable("GITHUB_REF");
     }
 
     public override bool PreventFetch() => true;