Fixes#1071
`TestRepoFromPath_Worktree` creates a throwaway temp repo and commits to it. On machines with `commit.gpgsign=true` in global git config, the commit fails with `No secret key`.
Override the global setting by setting `commit.gpgsign=false` in the temp repo's local config so the test is environment-independent.
Reviewed-on: https://gitea.com/gitea/tea/pulls/1072
Reviewed-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: Ross Golder <ross@golder.org>