Fix: fonts.css template doesn't correctly parse the style or weight options

[LewisDaleUK]

Modify the fonts.css.template logic, so that it correctly coerces the null values when font.style and font.weight are undefined.

The current logic is using null coersion (the ?? operator), which means that the value is only written when font.style is null - which of course then throws an error because it tries to read value from an undefined object.

Then, if font.style and font.weight are defined, the output is [object Object][object Object], because the actual statement is never reached.

Issue #, if available:

Description of changes:

Update the logic to use a ternary statement with empty strings as the fallbacks.

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[jorenbroekema]

Hey, this looks fine by me, could you maybe add a test and run npx changeset locally to create a human-readable changeset (patch bump is fine)?

[LewisDaleUK]

Hey, this looks fine by me, could you maybe add a test and run npx changeset locally to create a human-readable changeset (patch bump is fine)?

Added both now, let me know if they're okay/you need any more detail in them

[jorenbroekema]

I moved test file (we're a bit inconsistent about folder paths in lib versus tests) and used snapshots so it's easier to update in the future e.g. when we migrate to using tabs in v5 in all our formats, approved!