[MU4 Issue] Exported PDF files can have slightly wrong page size

When exporting a PDF file from MuseScore, the resulting PDF file can have a slightly wrong page size. For example, A4 is 210x297mm, but the exported file has 209,9x297mm. With Letter this seems to not occur.

(Could it be the case that MuseScore calculates page size in inches instead of milimeters?)

Tested in MuseScore 4 beta. Also happens in 3.6.2. Windows 10.

Steps to reprodute:

1. Open MuseScore
2. Create an empty score
3. Set page size
4. Export to PDF
5. Open the PDF file in a PDF reader that can show file properties

Why is this important?
This can be problematic (or at least not ideal) if you're assembling pages from different sources. For example, I'm assembling a teaching material with parts made in other apps, and a central part with scores from MuseScore. When merging the various PDF files, they'll have slightly different page sizes.

Reported also in https://musescore.org/en/node/337069 for MuseScore 3.6.