Add tests for writing spoken forms json from Talon

[pokey]

The functionality introduced in #1939 has no tests. We'd like to add tests by using the test context to set csv overrides dir setting to tmp dir, then override spokenforms json output location, then call the update function. Check output, then tweak csv, then check output again

We could also possibly use this mechanism instead of normalized_ctx, because spoken forms will be default when we do this. We'd want to remove all - prefixes on spoken forms to enable the ones that are off by default. But testing changes is prob a good idea anyway, as suggested above