skip checkRepoConfigInaccessible when git directory specified explicitly

skip checkRepoConfigInaccessible when git directory specified explicitly

Fix a reversion that prevented git-annex from working in a repository when
--git-dir or GIT_DIR is specified to relocate the git directory to
somewhere else. (Introduced in version 10.20220525)

checkRepoConfigInaccessible could still run git config --list, just passing
--git-dir. It seems not necessary, because I know that passing --git-dir
bypasses git's check for repo ownership. I suppose it might be that git
eventually changes to check something about the ownership of the working
tree, so passing --git-dir without --work-tree would still be worth doing.
But for now this is the simple fix.

Sponsored-by: Nicholas Golder-Manning on Patreon