Fix(Git ignorecase=false): keep default_PDF.pdf, remove default_pdf.pdf (#947)

# Description

## Summary

<!--BRIEF description: DONT'T EXPLAIN the code: JUSTIFY what this PR is
for!-->

That damn PDF breaks my local repo bc it conflicts with my global
`ignorecase = false` git config

## Changes Made

<!--DESCRIBE the changes: tell the BIG STEPS, use a CHECKLIST to show
progress. You can explain below how the code works.-->

- [x] `rm default_pdf.pdf` (used once vs thrice for `default_PDF.pdf`)
- [ ] use only `default_PDF.pdf` in the codebase

<!--Don't touch thses two tags-->
<details>
<summary>

# Classification

</summary>

## Type of Change

- [x] 🐛 Bug fix (non-breaking change which fixes an issue)
- [ ] ✨ New feature (non-breaking change which adds functionality)
- [ ] 🔨 Refactor (non-breaking change that neither fixes a bug nor adds
a feature)
- [ ] 🔧 Infra CI/CD (changes to configs of workflows)
- [ ] 💥 BREAKING CHANGE (fix or feature that require a new minimal
version of the front-end)
- [x] 😶‍🌫️ No impact for the end-users

## Impact & Scope

- [ ] Core functionality changes
- [ ] Single module changes
- [ ] Multiple modules changes
- [ ] Database migrations required
- [x] Other:  <!--Not module-oriented: write something!-->

## Testing

- [x] 1. Tested this locally
- [ ] 2. Added/modified tests that pass the CI (or tested in a
downstream fork)
- [ ] 3. Tested in a deployed pre-prod
- [ ] 0. Untestable (exceptionally), will be tested in prod directly

## Documentation

- [ ] Updated [the docs](docs.myecl.fr) accordingly : <!--[Docs#0 -
Title](https://github.com/aeecleclair/myecl-documentation/pull/0)-->
- [ ] `"` Docstrings
- [ ] `#` Inline comments
- [x] No documentation needed

</details>

Author: Marc-Andrieu

assets/pdf/default_pdf.pdf

@@ -244,7 +244,7 @@ async def test_save_pdf_first_page_as_image() -> None:
         input_pdf_directory="test/pdf",
         output_image_directory="test/image",
         filename=valid_uuid,
-        default_pdf_path="assets/pdf/default_pdf.pdf",
+        default_pdf_path="assets/pdf/default_PDF.pdf",
     )
     assert Path(f"data/test/image/{valid_uuid}.jpg").is_file()