Add test demonstrating the problem

When there's a branch with the same name as the tag, the branch gets checked out
instead of the tag.

pkg/integration/tests/tag/checkout_when_branch_with_same_name_exists.go

@@ -0,0 +1,38 @@
+package tag
+
+import (
+	"github.com/jesseduffield/lazygit/pkg/config"
+	. "github.com/jesseduffield/lazygit/pkg/integration/components"
+)
+
+var CheckoutWhenBranchWithSameNameExists = NewIntegrationTest(NewIntegrationTestArgs{
+	Description:  "Checkout a tag when there's a branch with the same name",
+	ExtraCmdArgs: []string{},
+	Skip:         false,
+	SetupConfig:  func(config *config.AppConfig) {},
+	SetupRepo: func(shell *Shell) {
+		shell.EmptyCommit("one")
+		shell.NewBranch("tag")
+		shell.Checkout("master")
+		shell.EmptyCommit("two")
+		shell.CreateLightweightTag("tag", "HEAD")
+	},
+	Run: func(t *TestDriver, keys config.KeybindingConfig) {
+		t.Views().Tags().
+			Focus().
+			Lines(
+				Contains("tag").IsSelected(),
+			).
+			PressPrimaryAction() // checkout tag
+
+		t.Views().Branches().IsFocused().Lines(
+			/* EXPECTED:
+			Contains("HEAD detached at tag").IsSelected(),
+			Contains("master"),
+			Contains("tag"),
+			ACTUAL: */
+			Contains("* tag").DoesNotContain("HEAD detached").IsSelected(),
+			Contains("master"),
+		)
+	},
+})

pkg/integration/tests/test_list.go

@@ -245,6 +245,7 @@ var tests = []*components.IntegrationTest{
 	sync.PushWithCredentialPrompt,
 	sync.RenameBranchAndPull,
 	tag.Checkout,
+	tag.CheckoutWhenBranchWithSameNameExists,
 	tag.CreateWhileCommitting,
 	tag.CrudAnnotated,
 	tag.CrudLightweight,