Updating from MEI 4 to MEI 5 adds mensural attributes

[rettinghaus]

Describe the problem
When loading a mensural file with version="4.0.0" into Verovio (updating it to MEI 5 effectively) every mensur element gets an @dot and @sign added automatically.

To Reproduce
Steps to reproduce the behavior:

1. Load "mensural-001.mei" from the test suite
2. Save it back
3. See error

Expected behavior
Non mandatory attributes shouldn't be added just by loading/updating a file. @dot and @sign are not required for mensur in MEI 5 and shouldn't be added (at least not without throwing a warning/info).

Input data
"mensural-001.mei" from the test suite

Verovio information

• Verovio 5.0.0
• all bindings

[lpugin]

Verovio used to infer the (visual) sign and dot from tempus and prolation up to MEI 4.0. This is no longer the case, which is why values are added when upgrading the files. It is looking all fine to me, except for the files that need upgrading, obviously.