[PATCH] parser: Update reference to PatchComment

[Stephen Finucane]

On Sat, 2020-11-28 at 17:02 +0000, Stephen Finucane wrote:
> Commit 0686a736fbf6d869bd31bd135ba38080ac96de22 split out 'CoverLetter'
> from the old 'Submission' model, removing the common 'Comment' model in
> favour of distinct 'CoverComment' and 'PatchComment' models in the
> process. Unfortunately we misssed some references to the old model in
> the 'patchwork.parser' module. Correct these now, adding unit tests to
> prevent regressions.
> 
> Signed-off-by: Stephen Finucane <stephen at that.guru>
> Fixes: 0686a736 ("models: Split 'CoverLetter' from 'Submission'")
> Closes: #384

I've gone ahead and applied this straight off the bat, since it's obviously
correct.

Stephen