Adds a pre-commit hook for ggshield not in a CI environment

[iainsproat]

Description & motivation

Would like to run ggshield locally as part of a pre-commit step, but not in a CI environment. This pre-commit hook does that.

Changes:

• adds a pre-commit hook ggshield-not-ci

To-do before merge:

Screenshots:

Validation of changes:

Checklist:

• My pull request follows the guidelines in the Contributing guide?
• My pull request does not duplicate any other open Pull Requests for the same update/change?
• My commits are related to the pull request and do not amend unrelated code or documentation.
• My code follows a similar style to existing code.
• I have added appropriate tests.
• I have updated or added relevant documentation.

References