[BUG] Tests make assumptions about local git config

[stephenc]

Describe the bug
The tests assume that the default git branch for new repositories is called master and that git is not configured to sign all commits. As a result if you try to run the tests in an environment that is using main as the default branch for newly created repos and/or you try to run the tests where Git is configured to sign all commits, the tests fail.

To Reproduce
Steps to reproduce the behavior:

1. Edit ~/.gitconfig and add

[init]
    defaultBranch = main
[user]
    ...
    signingkey = ....

Whereby you change the default branch and add a signingkey to the user

2. Run the tests

Expected behavior
A clear and concise description of what you expected to happen.

The tests should pass

Additional context
Add any other context about the problem here.

[stephenc]

I think this just requires the appropriate use if git init -b master in a couple of places as well as either adding --no-gpg-sign to the git commit commands in the tests or setting the local user config consistently as is done in helper's git_init