Always show branch heads in diff pane

The first line of the diff pane would show branch heads (e.g.

  commit dd9100ccc8b69a8b14b21a84e34854b5acfb871a (mybranch, origin/mybranch)

only when a pager is used. The reason is that the default of the --decorate
option to git show is "auto", which means to show the decoration only when
output goes to a tty. Lazygit uses a pty only when a pager is used, so the
decoration wouldn't show when no pager is used.

Since the branch head annotation is useful and we always want to see it, force
it by explicitly passing --decorate.

pkg/commands/git_commands/commit.go

@@ -212,6 +212,7 @@ func (self *CommitCommands) ShowCmdObj(sha string, filterPath string, ignoreWhit
 		Arg("--color="+self.UserConfig.Git.Paging.ColorArg).
 		Arg(fmt.Sprintf("--unified=%d", contextSize)).
 		Arg("--stat").
+		Arg("--decorate").
 		Arg("-p").
 		Arg(sha).
 		ArgIf(ignoreWhitespace, "--ignore-all-space").

pkg/commands/git_commands/commit_test.go

@@ -212,28 +212,28 @@ func TestCommitShowCmdObj(t *testing.T) {
 			filterPath:       "",
 			contextSize:      3,
 			ignoreWhitespace: false,
-			expected:         []string{"show", "--submodule", "--color=always", "--unified=3", "--stat", "-p", "1234567890"},
+			expected:         []string{"show", "--submodule", "--color=always", "--unified=3", "--stat", "--decorate", "-p", "1234567890"},
 		},
 		{
 			testName:         "Default case with filter path",
 			filterPath:       "file.txt",
 			contextSize:      3,
 			ignoreWhitespace: false,
-			expected:         []string{"show", "--submodule", "--color=always", "--unified=3", "--stat", "-p", "1234567890", "--", "file.txt"},
+			expected:         []string{"show", "--submodule", "--color=always", "--unified=3", "--stat", "--decorate", "-p", "1234567890", "--", "file.txt"},
 		},
 		{
 			testName:         "Show diff with custom context size",
 			filterPath:       "",
 			contextSize:      77,
 			ignoreWhitespace: false,
-			expected:         []string{"show", "--submodule", "--color=always", "--unified=77", "--stat", "-p", "1234567890"},
+			expected:         []string{"show", "--submodule", "--color=always", "--unified=77", "--stat", "--decorate", "-p", "1234567890"},
 		},
 		{
 			testName:         "Show diff, ignoring whitespace",
 			filterPath:       "",
 			contextSize:      77,
 			ignoreWhitespace: true,
-			expected:         []string{"show", "--submodule", "--color=always", "--unified=77", "--stat", "-p", "1234567890", "--ignore-all-space"},
+			expected:         []string{"show", "--submodule", "--color=always", "--unified=77", "--stat", "--decorate", "-p", "1234567890", "--ignore-all-space"},
 		},
 	}