From: Harald Nordgren <haraldnordgren@gmail.com>

The "verify signed tag fails when public key is not present" test
deletes gpghome to lose the key, and this sometimes fails on Alpine
with

    rm: can't remove 'gpghome/S.gpg-agent.extra': No such file or directory

Point GNUPGHOME at an unused directory for the verification, which is
how t7510 checks a signature whose key is unknown.

Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>

Submitted-As: https://lore.kernel.org/git/pull.2443.git.git.1791450465178.gitgitgadget@gmail.com