fix master regex after adding main, add/modify tests to cover that change

Author: thetimbecker

docs/input/docs/configuration.md

@@ -283,7 +283,7 @@ upgrade.
 ```yaml
 branches:
   master:
-    regex: ^master|main$
+    regex: ^master$|^main$
     mode: ContinuousDelivery
     tag: ''
     increment: Patch

src/GitVersionCore.Tests/Configuration/ConfigProviderTests.CanWriteOutEffectiveConfiguration.approved.txt

@@ -31,7 +31,7 @@ branches:
     increment: Patch
     prevent-increment-of-merged-branch-version: true
     track-merge-target: false
-    regex: ^master|main$
+    regex: ^master$|^main$
     source-branches:
     - develop
     - release

src/GitVersionCore.Tests/IntegrationTests/OtherScenarios.cs

@@ -60,25 +60,25 @@ public void AllowHavingVariantsStartingWithMaster()
         [Test]
         public void AllowHavingMainInsteadOfMaster()
         {
-            var config = new Config();
-            config.Branches.Add("master", new BranchConfig
-            {
-                Regex = "main",
-                VersioningMode = VersioningMode.ContinuousDelivery,
-                Tag = "useBranchName",
-                Increment = IncrementStrategy.Patch,
-                PreventIncrementOfMergedBranchVersion = true,
-                TrackMergeTarget = false,
-                SourceBranches = new HashSet<string>()
-            });
-
             using var fixture = new EmptyRepositoryFixture();
             fixture.Repository.MakeACommit();
             Commands.Checkout(fixture.Repository, fixture.Repository.CreateBranch("develop"));
             Commands.Checkout(fixture.Repository, fixture.Repository.CreateBranch("main"));
             fixture.Repository.Branches.Remove(fixture.Repository.Branches["master"]);
 
-            fixture.AssertFullSemver("0.1.0-1+0", config);
+            fixture.AssertFullSemver("0.1.0+0");
+        }
+
+        [Test]
+        public void AllowHavingVariantsStartingWithMain()
+        {
+            using var fixture = new EmptyRepositoryFixture();
+            fixture.Repository.MakeACommit();
+            fixture.Repository.MakeATaggedCommit("1.0.0");
+            fixture.Repository.MakeACommit();
+            Commands.Checkout(fixture.Repository, fixture.Repository.CreateBranch("mainfix"));
+
+            fixture.AssertFullSemver("1.0.1-mainfix.1+1");
         }
 
         [Test]

src/GitVersionCore/Model/Configuration/Config.cs

@@ -115,7 +115,7 @@ public override string ToString()
         public const string HotfixBranchRegex = "^hotfix(es)?[/-]";
         public const string SupportBranchRegex = "^support[/-]";
         public const string DevelopBranchRegex = "^dev(elop)?(ment)?$";
-        public const string MasterBranchRegex = "^master|main$";
+        public const string MasterBranchRegex = "^master$|^main$";
         public const string MasterBranchKey = "master";
         public const string ReleaseBranchKey = "release";
         public const string FeatureBranchKey = "feature";