Refs issue #128 (Metal Gear's item 4), the plain-error half.
oh proposal create in a wiki checkout failed with HTTP 404: no such repository, though pushing works. For anyone who can read the repository, the API now answers:
OWNER/NAME.wiki is the wiki of OWNER/NAME: it is cloned and pushed with oxy, and takes no proposals, issues or runs; to publish a bookmark, merge it into main (oxy merge BOOKMARK on main) and push main
Others still get "no such repository", so private repositories don't leak. issue #128 stays open for real wiki proposals.
Test: api_webhooks_and_checks extended. Hub gate green (162 tests, clippy, fmt).