Remove deprecated `ruff` rule `E999` from `ruff.toml`

[EGJ-Moorington]

The ruff.toml file generated by the template includes a check for rule E999 (sintax-error), which has been removed. According to the documentation:

Syntax errors will always be shown regardless of whether this rule is selected or not.

Using this rule produces an error when running the ruff pre-commit hook:

ruff (legacy alias)......................................................Failed

• hook id: ruff
• exit code: 2

ruff failed
Cause: Rule E999 was removed and cannot be selected.