fix tab x button being obscured by tab title text

Need to explicitly pop it in front of the tab text layer so that
the button is physically rendered on top of the tab title.

refs: https://github.com/wez/wezterm/issues/2269

docs/changelog.md

@@ -68,6 +68,7 @@ As features stabilize some brief notes about them will accumulate here.
 * Shift-F1 through F4 generated different encoding than xterm [#2263](https://github.com/wez/wezterm/issues/2263)
 * X11/Wayland: apps that extract the `Exec` field from wezterm.desktop (such as thunar, Dolphin and others) can now simply concatenate the command line they want to invoke, and it will spawn in the their current working directory. Thanks to [@Anomalocaridid](https://github.com/Anomalocaridid)! [#2271](https://github.com/wez/wezterm/pull/2271) [#2103](https://github.com/wez/wezterm/issues/2103) 
 * [gui-startup](config/lua/gui-events/gui-startup.md) now passes a [SpawnCommand](config/lua/SpawnCommand.md) parameter representing the `wezterm start` command arguments.
+* Tab `x` button is no longer obscured by tab title text for long tab titles [#2269](https://github.com/wez/wezterm/issues/2269)
 
 #### Updated
 * Bundled harfbuzz to 4.4.1

wezterm-gui/src/termwindow/render.rs

@@ -719,6 +719,9 @@ impl super::TermWindow {
                                     },
                                 },
                             )
+                            // Ensure that we draw our background over the
+                            // top of the rest of the tab contents
+                            .zindex(1)
                             .vertical_align(VerticalAlign::Middle)
                             .float(Float::Right)
                             .item_type(UIItemType::CloseTab(tab_idx))