encoding: override ASCII to default encoding

[tmorrell]

:heart: Thank you for your contribution!

Description

This PR resolves an issue with the text file previewer, where the encoding is detected as ASCII even though the file (and default) has utf8 characters beyond the detection range. Resolves https://github.com/inveniosoftware/invenio-previewer/issues/176 and partially resolves https://github.com/inveniosoftware/invenio-app-rdm/issues/1864

Checklist

Ticks in all boxes and 🟢 on all GitHub actions status checks are required to merge:

• [x] I'm aware of the code of conduct.
• [x] I've created logical separate commits and followed the commit message format.
• [ ] I've added relevant test cases.
• [ ] I've added relevant documentation.
• [ ] I've marked translation strings (for relevant code).
• [ ] I've followed the CSS/JS and React guidelines (for relevant code).
• [ ] I've followed the web accessibility guidelines (for relevant code).
• [ ] I've followed the user interface guidelines (for relevant code).
• [ ] I've identified the copyright holder(s) and updated copyright headers for touched files (>15 lines contributions).
• [x] I've NOT included third-party code (copy/pasted source code or new dependencies).

Third-party code

If you've added third-party code (copy/pasted or new dependencies), please reach out to an architect.

Reminder

By using GitHub, you have already agreed to the GitHub’s Terms of Service including that:

1. You license your contribution under the same terms as the current repository’s license.
2. You agree that you have the right to license your contribution under the current repository’s license.