Implement some form of font regression/e2e tests

[HarveyPeachey]

Is your feature request related to a problem? Please describe.
When carrying out the font replacement work for Bengali, Sinhala and Tamil, it was noticed that there was next to no regression tests for these services, the only test that did fail was a snapshot for Most Read which detected a change in a single font size change. We should have some coverage for regression of fonts that aren't just a LTR and RTL service which are used in a majority of our snapshot testing.

Describe the solution you'd like
Implement a form of regression tests that either explicitly check for fonts that should exist for each service. There could also be some form of e2e to detect if a font has loaded on a page correctly? Try and pair with a tester to come up with the best solution.

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Testing notes
[Tester to complete]

Dev insight: Will Cypress tests be required or are unit tests sufficient? Will there be any potential regression? etc

• This feature is expected to need manual testing.

Checklist

• (BBC contributors only) This issue follows the repository use guidelines

Additional context
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