changelog: fix the diverted opener to accept more kwargs
The current code prevent the use of `atomictemp` file with the changelog
opener. I do not see a good reason for this limitation.
Differential Revision: https://phab.mercurial-scm.org/D7831
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IncludeCategories:
- Regex: '^<'
Priority: 1
- Regex: '^"'
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