git 2.34.0: Behavior of `**` in gitignore is different from previous versions.

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Please answer the following questions to help us understand your issue.

What did you do before the bug happened? (Steps to reproduce your issue)
Consider the following project structure
- data
  - data1
    - file1
    - file1.txt
  - data2
    - file2
    - file2.txt
- .gitignore


`.gitignore` is as follows:

data/**
!data/**/
!data/**/*.txt

What did you expect to happen? (Expected behavior)

I expect all files in `data` folder to be ignored except `.txt` files.

What happened instead? (Actual behavior)

`file1` and `file2` are not ignored.
Here is the `check-ignore` output:

$ git check-ignore -v data/data1/file1
.gitignore:2:!/data/**/ data/data1/file1

What's different between what you expected and what actually happened?
It seems that the behavior of `**` in gitignore is different from
previous versions.

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 2.34.0
cpu: x86_64
no commit associated with this build
sizeof-long: 8
sizeof-size_t: 8
shell-path: /bin/sh
uname: Linux 5.15.2-arch1-1
compiler info: gnuc: 11.1
libc info: glibc: 2.33
$SHELL (typically, interactive shell): /usr/bin/zsh


[Enabled Hooks]