git apply: Not reliably working as `patch` replacement when `.git` file/directory exists

Hello Git developers,

thank your for that great developer tool!
I noticed a behavior with git apply which I assume is a bug. So I am
going to report it here.

Thanks for reading,
Deniz Bahadir


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

1. `git clone` a Git repository which contains a Git submodule.
2. Initialize the submodule by using `git submodule update --init`.
3. Change into that Git submodule directory and create a patch for a
   file in it.
   (Note: Here we assume the directory is called `submodule` and the
   to-be-patched file is called `file.txt`.)

   cd submodule
   echo "extra-tokens" >> file.txt
   git diff -u file.txt > file.txt.patch
   git checkout file.txt

4.a) Copy the directory of this Git submodule into another directory
     which itself is not located in or beneath a directory under Git
     control.
4.b) Same as 4.a) but additionally remove the `.git` file in that
     copied directory.
4.c) Rename the directory of this submodule but do not inform Git
     about it (e.g. do a `mv submodule submodule_renamed`).
4.d) Same as 4.c) but additionally remove the `.git` file in that
     moved directory.
5. For each directory created under step 4 change into it and run:

   git apply --unsafe-paths -v file.txt.patch

## What did you expect to happen? (Expected behavior)

I expected all four different scenarios to succeed and to successfully
patch `file.txt` in step 5.


## What happened instead? (Actual behavior)

Case 5.a) fails with the following message:

fatal: not a git repository: /tmp/submodule/../.git/modules/submodule

Case 5.b) succeeds with the following message:

Checking patch file.txt...
Applied patch file.txt cleanly.

Case 5.c) fails with the following message:

fatal: cannot chdir to '../../../submodule': No such file or directory

Case 5.d) fails with the following message:

Skipped patch 'file.txt'.

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

I would have expected that option `--unsafe-paths` allows me to patch
any file using `git apply` not matter where the directory is located
and whether there is a `.git` file or directory in any of its parent
directories or not.
That would have allowed me to use `git apply --unsafe-paths` as an
alternative to `patch` (which might not be available on all platforms)
as written on `git apply`'s man page.


## Anything else you want to add:

Alternatively, maybe it would be better if `git apply` provides an
extra option `--simulate-patch` or something similar which really
works as a `patch` replacement in all situations (and does not
consider `.git` files or directories at all).


## Additional system info.

[System Info]
git version:
git version 2.33.1.windows.1 and 2.25.1 (ubuntu)
cpu: x86_64
sizeof-long: 4
sizeof-size_t: 8
shell-path: /bin/sh