Cannot load EVEREST_SAVEPATH variable from everest-env.txt file

### My mods and Everest install are up to date

Yes

### I have recreated the bug with only Everest OR a minimum number of mods enabled

No

### Describe the bug

Hi, I recently switched to Linux, and the save location is not the same as on Windows. This is why I need to use the environment variable EVEREST_SAVEPATH.

Unfortunately, I was only able to use it by using an export command and then opening the game from a terminal:
```bash
export EVEREST_SAVEPATH=/run/media/Pilogoude/HDD-1To/Games/itch.io/everest/
switcherooctl launch /run/media/Pilogoude/HDD-1To/Games/itch.io/everest/Celeste
```
_(Note: I am using a laptop and I need to use `switcherooctl launch` to run the game on my dedicated graphics card instead of the integrated one)._

I cannot make EVEREST_SAVEPATH work with the everest-env.txt file, even though it is placed correctly in the game installation root folder (in the same location as the existing everest-launch.txt file). Inside the file, I wrote:
```plaintext
EVEREST_SAVEPATH=/run/media/Pilogoude/HDD-1To/Games/itch.io/everest/
```
I am sure that I formatted my everest-env.txt file correctly, because I already asked a question about it [here](https://github.com/EverestAPI/Everest/issues/1131). So I am coming here now because the game still does not take my environment variable into account.

_I am playing the native Linux version of Celeste from itch.io._

### Steps to reproduce

1. Create a file named everest-env.txt in the game installation root folder, at the same location as everest-launch.txt
2. Inside everest-env.txt, add the following line:`EVEREST_SAVEPATH=/run/media/Pilogoude/HDD-1To/Games/itch.io/everest/`
3. Launch the game from a terminal that does not have the EVEREST_SAVEPATH environment variable exported, or from a desktop entry or file explorer

### Expected behavior

The game should read the everest-env.txt file and apply the EVEREST_SAVEPATH environment variable, and should then load and save the progress in the specified custom folder instead of the default Linux save location `/home/Pilogoude/.local/share/Celeste/`.

### Operating System

CachyOS

### Everest Version

6314

### Mods required to reproduce

_No response_

### Additional context

_No response_

Start by locating the code that reads everest-env.txt and everest-launch.txt during native Linux startup. Reproduce the issue without EVEREST_SAVEPATH exported, then verify that the value from everest-env.txt is applied and that saves use the specified folder.

Written by the indexing model from the issue text.