fix: sanitize labels correctly when using enviornment variables

src/GitVersion.Configuration.Tests/Configuration/ConfigurationExtensionsTests.cs

@@ -143,4 +143,24 @@ public void EnsureGetBranchSpecificLabelThrowsWhenEnvVarMissing()
         Should.Throw<ArgumentException>(() =>
             effectiveConfiguration.GetBranchSpecificLabel(ReferenceName.FromBranchName(BranchName), null, environment));
     }
+
+    [TestCase("case-00/my-branch", "case-00-my-branch")]
+    [TestCase("my-branch", "my-branch")]
+    [TestCase("my_branch/valid", "my-branch-valid")]
+    public void EnsureGetBranchSpecificLabelReturnsValidLabelForEnvironmentVariables(string variable, string expectedLabel)
+    {
+        var environment = new TestEnvironment();
+        environment.SetEnvironmentVariable("GITHUB_HEAD_REF", variable);
+
+        var configuration = GitFlowConfigurationBuilder.New
+            .WithoutBranches()
+            .WithBranch("feature/test-feature", builder => builder
+                .WithLabel("{env:GITHUB_HEAD_REF}")
+                .WithRegularExpression(@"^features?[\/-](?<BranchName>.+)"))
+            .Build();
+
+        var effectiveConfiguration = configuration.GetEffectiveConfiguration(ReferenceName.FromBranchName("feature/test-feature"));
+        var actual = effectiveConfiguration.GetBranchSpecificLabel(ReferenceName.FromBranchName("feature/test-feature"), null, environment);
+        actual.ShouldBe(expectedLabel);
+    }
 }

src/GitVersion.Core/Core/RegexPatterns.cs

@@ -34,6 +34,9 @@ internal static partial class RegexPatterns
     [StringSyntax(StringSyntaxAttribute.Regex, Options)]
     internal const string SanitizeNameRegexPattern = "[^a-zA-Z0-9-]";
 
+    [StringSyntax(StringSyntaxAttribute.Regex, Options)]
+    internal const string SanitizeLabelRegexPattern = "[^a-zA-Z0-9-.]";
+
 #if NET9_0_OR_GREATER
     [GeneratedRegex(SwitchArgumentRegexPattern, Options)]
     public static partial Regex SwitchArgumentRegex { get; }

src/GitVersion.Core/Extensions/ConfigurationExtensions.cs

@@ -133,7 +133,8 @@ private static bool ShouldBeIgnored(ICommit commit, IIgnoreConfiguration ignore)
             var effectiveBranchName = branchNameOverride ?? branchName;
             var labelPlaceholders = BuildLabelPlaceholders(configuration.RegularExpression, effectiveBranchName);
 
-            return label.FormatWith(labelPlaceholders, environment);
+            return label.FormatWith(labelPlaceholders, environment)
+                .RegexReplace(RegexPatterns.SanitizeLabelRegexPattern, "-");
         }
 
         public TaggedSemanticVersions GetTaggedSemanticVersion()