regression: remote-build fails when project is not in a git directory

[mr-cal]

Bug Description

In snapcraft 8.0.1, remote-build is now failing if the project is not in a git repository.

This failure is occurring in the weekly spread tests: https://github.com/snapcore/snapcraft/actions/runs/7469897740/job/20327823910#step:5:36

This check is causing snapcraft to fail and preempts all the code that automatically initializes a git repository in the temporary work directory.

To Reproduce

mkdir tmp
pushd tmp
snapcraft init
snapcraft remote-build
popd

Environment

n/a

snapcraft.yaml

n/a

Relevant log output

2024-01-10 03:26:29.754 remote-build error: The Git repository is invalid for remote build.
Could not find a git repository in '.'

Additional context

No response

[mr-cal]

Per Sergio, this is an intentional decision for the following reason:
If a user builds destructively locally and is not in a git repo, snapcraft will add the parts, stage, and prime directory to the git repo it initializes. This could cause the remote-builder to re-use these directories instead of doing a clean build.

The path forward is to adjust the failing spread test and improve the error message.

[cmatsuoka]

Per Sergio, this is an intentional decision for the following reason: If a user builds destructively locally and is not in a git repo, snapcraft will add the parts, stage, and prime directory to the git repo it initializes. This could cause the remote-builder to re-use these directories instead of doing a clean build.

This could also be handled by ignoring the work directories when creating the git repo (we use a similar approach when copying to the part src directory).