Fzf commands (:Files) open new shell process in Git-bash Windows

- [x] I have fzf 0.23.0 or above
- [x] I have read through https://github.com/junegunn/fzf.vim/blob/master/README.md
- [x] I have read through https://github.com/junegunn/fzf/blob/master/README-VIM.md
- [x] I have read through the manual page of fzf (`man fzf`)
- [x] I have searched through the existing issues

`:Files`/`:FZF` in vim within git-bash shell is opening new sh.exe window instead of within vim window.

I tried setting fzf_layout in .vimrc (as in [Fzf Vim Readme](https://github.com/junegunn/fzf/blob/master/README-VIM.md): `let g:fzf_layout = { 'down': '30%' }` ) but still getting same behaviour of new shell process in new window, while vim display goes blank

Expected behavior: fzf search window opens within same vim process

Vim Version:

```
VIM - Vi IMproved 8.2 (2019 Dec 12, compiled Sep 21 2021 16:13:20)
Included patches: 1-3441
Compiled by
Huge version without GUI. Features included (+) or not (-):
+acl +file_in_path +mouse_urxvt -tag_any_white
+arabic +find_in_path +mouse_xterm -tcl
+autocmd +float +multi_byte +termguicolors
+autochdir +folding +multi_lang +terminal
-autoservername -footer -mzscheme +terminfo
-balloon_eval +fork() +netbeans_intg +termresponse
+balloon_eval_term +gettext +num64 +textobjects
-browse -hangul_input +packages +textprop
++builtin_terms +iconv +path_extra +timers
+byte_offset +insert_expand +perl/dyn +title
+channel +ipv6 +persistent_undo -toolbar
+cindent +job +popupwin +user_commands
-clientserver +jumplist +postscript +vartabs
+clipboard +keymap +printer +vertsplit
+cmdline_compl +lambda +profile +virtualedit
+cmdline_hist +langmap -python +visual
+cmdline_info +libcall +python3/dyn +visualextra
+comments +linebreak +quickfix +viminfo
+conceal +lispindent +reltime +vreplace
+cryptv +listcmds +rightleft +wildignore
+cscope +localmap +ruby/dyn +wildmenu
+cursorbind -lua +scrollbind +windows
+cursorshape +menu +signs +writebackup
+dialog_con +mksession +smartindent -X11
+diff +modify_fname -sodium -xfontset
+digraphs +mouse -sound -xim
-dnd -mouseshape +spell -xpm
-ebcdic +mouse_dec +startuptime -xsmp
+emacs_tags -mouse_gpm +statusline -xterm_clipboard
+eval -mouse_jsbterm -sun_workshop -xterm_save
+ex_extra +mouse_netterm +syntax
+extra_search +mouse_sgr +tag_binary
-farsi -mouse_sysmouse -tag_old_static
system vimrc file: "/etc/vimrc"
user vimrc file: "$HOME/.vimrc"
2nd user vimrc file: "~/.vim/vimrc"
user exrc file: "$HOME/.exrc"
defaults file: "$VIMRUNTIME/defaults.vim"
fall-back for $VIM: "/etc"
f-b for $VIMRUNTIME: "/usr/share/vim/vim82"
Compilation: gcc -c -I. -Iproto -DHAVE_CONFIG_H -I/usr/include/ncursesw -march=x86-64 -mtune=generic -O2 -pipe -D_REENTRANT -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=1
Linking: gcc -L. -pipe -fstack-protector-strong -pipe -Wl,--as-needed -o vim.exe -lm -lncursesw -liconv -lacl -lintl -Wl,--enable-auto-import -Wl,--export-all-symbols -Wl,--enable-auto-image-base -fstack-protector-strong -L/usr/lib/perl5/core_perl/CORE -lperl -lpthread -ldl -lcrypt
```

Minimal config with same issue: (ran with `vim -Nu config.txt`

```
set nocompatible hidden laststatus=2

if !filereadable('/tmp/plug.vim')
silent !curl --insecure -fLo /tmp/plug.vim
\ https://raw.githubusercontent.com/junegunn/vim-plug/master/plug.vim
endif
source /tmp/plug.vim
call plug#begin('/tmp/plugged')
Plug 'junegunn/fzf', { 'do': './install --bin' }
Plug 'junegunn/fzf.vim'
call plug#end()
let g:fzf_layout = { 'down': '30%' }

autocmd VimEnter * PlugClean! | PlugUpdate --sync
```