Running `git-annex lookupkey` while in a subdirectory of a git-annex repository does not work, regardless of whether the supplied path is relative to the current directory or the root of the repository.

### What steps will reproduce the problem?

[[!format sh """
git init
git-annex init
git-annex addurl --file latex/lshort.pdf https://tobi.oetiker.ch/lshort/lshort.pdf
cd latex
git-annex lookupkey lshort.pdf  # Fails!
git-annex lookupkey latex/lshort.pdf  # Fails!
cd ..
git-annex lookupkey latex/lshort.pdf  # Succeeds
"""]]


### What version of git-annex are you using? On what operating system?

8.20211011 on macOS 11.6

[[!meta author=jwodder]]

> [[fixed|done]] --[[Joey]]
