Include "history.csv" in gitignore

[j-signorelli]

For non-restart SU2 simulations, a history.csv file is outputted. This PR simply ensures that these are ignored.

Checklist:

• I added a summary of any user-facing changes (compared to the last release) in the changelog-entries/<PRnumber>.md.
• I will remember to squash-and-merge, providing a useful summary of the changes of this PR.

[MakisH]

Perfect, thank you! 🤗

I don't think we really need a changelog entry for this.