Renaming a file by changing the casing of the letters in a FAT32 partition is impossible

# Prerequisites
- [x] I have searched open and closed issues for duplicates.

# Describe the error

Renaming a file by changing the casing of the letters in a FAT32 partition is impossible.

## To reproduce

1. Open Files.
2. Navigate to a partition which is formatted using FAT32.
3. Create a file “Essai”.
4. Rename the file to “essai”.
5. The application says that a file with this name already exists.

## Expected behaviour

The user is not told that an existing file with this name already exists. Instead, the casing of the file or folder is changed to the new one.

I suppose that the correct term would be that the new case is [preserved](https://en.wikipedia.org/wiki/Case_preservation).

## Screenshots or screen recordings

[Screen recording](https://github.com/elementary/files/files/4144363/Renaming.a.file.by.changing.the.casing.of.the.letters.in.a.FAT32.partition.is.impossible.zip)

# Platform information


- [ ] I'm using the latest version from git that I've manually compiled
- [x] I'm using the latest released stable version

Language: French
Keyboard: English (US) - English (Dvorak intl., with dead keys)
Location: Paris

The testing system is installed on a small partition on a ThinkPad T470 laptop on which UEFI Secure Boot is disabled. Aside from specifying the language, keyboard, location, initial user, and the specific partition in which to install elementary OS, all of the default settings were used during the installation. No Internet connection was used during the installation. The only system-wide changes which have been made after the installation are that the system connects to the Internet by wi-fi via a Linksys WRT54GL Wireless Router and that [Screen Recorder](https://appcenter.elementary.io/com.github.mohelm97.screenrecorder/) has been installed via AppCentre.

# Additional context

Before this test was performed, the following steps were followed:

1. All system-wide changes from previous tests were reverted.
2. All system components were updated via the blue “Update All” button in AppCentre.
3. A new administrator user named “Essai” or “Essai 2” was created with the password “komalleana”.
4. The current user was logged out and the new user was logged in.
5. The old user was deleted, the screen resolution was set to 800x600 at 60 Hz, tap clicking was disabled, and the touchpad pointer speed was set to the maximal value.
6. The computer was rebooted.
6. The test user was logged in.