misleading message printed when worktree add fails

Thank you for filling out a Git bug report! Please answer the following questions to help us understand your issue.

What did you do before the bug happened? (Steps to reproduce your issue)

run `git worktree add <path> <branch>`, where <branch> is an already checked-out branch

What did you expect to happen? (Expected behavior)

fail to create worktree

What happened instead? (Actual behavior)

worktree was not created, but a confusing message was printed: "Preparing worktree (checking out '<branch>')"

What's different between what you expected and what actually happened?

The printed message seems to indicate that the command was a success, when in fact it was not

Anything else you want to add:

Please review the rest of the bug report below. You can delete any lines you don't wish to share.

[System Info] git version: git version 2.33.1.windows.1 cpu: x86_64 built from commit: 05d80adb775077d673fab685009ede4a1003ed92 sizeof-long: 4 sizeof-size_t: 8 shell-path: /bin/sh feature: fsmonitor--daemon uname: Windows 10.0 18363 compiler info: gnuc: 10.3 libc info: no libc information available $SHELL (typically, interactive shell): C:\Program Files\Git\usr\bin\bash.exe