"I" character getting inserted when calling :Files! :Buffers!

- [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

Hello!

Could someone please help me narrow down whether this issue is coming from vim or fzf.vim? Problem description, behavior, environment setup, and steps I took listed below.

# Problem

I am seeing the I character get automatically inserted when I invoke :Files! or :Buffers! command.
Even in this minimal configuration, the bug occured :
`
vim -Nu <(curl https://gist.githubusercontent.com/junegunn/6936bf79fedd3a079aeb1dd2f3c81ef5/raw)
`
I'm launching vim in Gnome Terminal version 3.40.3
(Using VTE version 0.66.0 +BIDI +GNUTLS +ICU -SYSTEMD)

Thanks for your help !

Start by reproducing :Files! and :Buffers! with the minimal Vim configuration command given in the issue, using the reported Gnome Terminal environment. Compare the commands with and without ! and verify that the stray I character no longer appears; the issue does not name a source file or test.

Written by the indexing model from the issue text.