Add code 2561 to known errors

[vkarpov15]

Followup to #202 and #204. After upgrading in Automattic/mongoose#14221 to tsd@0.30, I started getting the following errors:

  test/types/base.test.ts:61:29
  ✖   61:2   Found an error that tsd does not currently support (ts2353), consider creating an issue on GitHub.                                                                                                                                                                                                                                                               
  ✖   61:29  Object literal may only specify known properties, and invalid does not exist in type { allowDiskUse?: boolean | undefined; applyPluginsToChildSchemas?: boolean | undefined; applyPluginsToDiscriminators?: boolean | undefined; autoCreate?: boolean | undefined; autoIndex?: boolean | undefined; ... 21 more ...; translateAliases?: boolean | undefined; }.  

  test/types/models.test.ts:350:10
  ✖  346:2   Found an error that tsd does not currently support (ts2561), consider creating an issue on GitHub.                                                                                                                                                                                                                                                               
  ✖  350:10  Object literal may only specify known properties, but test does not exist in type OptionalId<{ testy: string; }>. Did you mean to write testy?                                                                                                                                                                                                                   

  4 errors

Why is 2561 a separate diagnostic code from 2353 even though the error message only differs "and" -> "but"? No idea. But this seems to fix the issue. I'm also open to suggestions for a better name than ObjectLiteralMayOnlySpecifyKnownProperties2.