Add support for Czech perfective verbs

The template was provided by [[User:Adrijaned]] [1] and [[User:Strepon]] [2]
at [[Wikidata:Wikidata Lexeme Forms/Czech]] [3] – thank you!

One of the tests needs an adjustment – this template has two examples
for different forms that are legitimately identical (at least, English
Wiktionary confirms that „zazpívala“ is both the feminine singular and
neuter plural active/past participle of „zazpívat“). This is extracted
into a set of ambiguous examples (though for now it only has one item),
in case this happens again later.

[1]: https://www.wikidata.org/wiki/User:Adrijaned
[2]: https://www.wikidata.org/wiki/User:Strepon
[3]: https://www.wikidata.org/wiki/Wikidata:Wikidata_Lexeme_Forms/Czech