[opentype/monospace] Ensure check works with monospace OTF fonts

[PeterDekkers]

Description

Fixes #5040

The opentype/monospace returned an ERROR status for monospace OTF fonts. This is because it tries to access the glyf table, which does not exist. The only reason the glyf table is accessed is to get the glyph names. To enable this to work for OTF and TTF alike, I instead used the TTFont.getGlyphNames() method.

I tried to add a monospace OTF font to the unit tests, but unfortunately I couldn't find an open source monospace OTF that would pass all of the checks. Maybe someone can recommend a suitable OTF file to use?

Checklist

• update CHANGELOG.md
• wait for the tests to pass
• request a review

[felipesanches]

Can you please update CHANGLOG.md?

You can add an entry under a new section:

Upcoming release v1.1.1 (2025-Oct-?)

Changes to existing checks

On the OpenType profile

• [check-id]: something something (PR [opentype/monospace] Ensure check works with monospace OTF fonts #5051)

Here the raw markdown code:

## Upcoming release v1.1.1 (2025-Oct-?)
### Changes to existing checks
#### On the OpenType profile
  - **[check-id]**: something something (PR #5051)

[PeterDekkers]

Thank you @felipesanches, I've updated CHANGELOG.md.

Also, I've just signed the Google CLA.