auto_update: Fix Windows installer task arguments syntax (#50464)

- The Inno Setup installer requires tasks to be specified with the
`/MERGETASKS` flag instead of bare arguments.
- Removed the `quicklaunchicon` task as it’s no longer relevant for
modern Windows 10 and up.

Ref: https://zed.dev/docs/installation#windows-1
Ref: https://documentation.help/Inno-Setup/topic_setupcmdline.htm

Closes #47570.

Before you mark this PR as ready for review, make sure that you have:
- [ ] Added a solid test coverage and/or screenshots from doing manual
testing
- [x] Done a self-review taking into account security and performance
aspects
- [x] Aligned any UI changes with the [UI
checklist](https://github.com/zed-industries/zed/blob/main/CONTRIBUTING.md#uiux-checklist)

Release Notes:

- Fixed Windows installer task arguments syntax

crates/auto_update/src/auto_update.rs

@@ -1109,8 +1109,7 @@ async fn install_release_windows(downloaded_installer: &Path) -> Result<Option<P
     let mut cmd = new_command(downloaded_installer);
     cmd.arg("/verysilent")
         .arg("/update=true")
-        .arg("!desktopicon")
-        .arg("!quicklaunchicon");
+        .arg("/MERGETASKS=!desktopicon");
     let output = cmd.output().await?;
     anyhow::ensure!(
         output.status.success(),