[flake8-pytest-style] Add a space after comma in CSV output (PT006) (#12853)

## Summary

See #12703. This only addresses the first bullet point, adding a space
after the comma in the suggested fix from list/tuple to string.

## Test Plan

Updated the snapshots and compared.

crates/ruff_linter/src/rules/flake8_pytest_style/rules/parametrize.rs

@@ -292,7 +292,7 @@ fn elts_to_csv(elts: &[Expr], generator: Generator) -> Option<String> {
             .fold(String::new(), |mut acc, elt| {
                 if let Expr::StringLiteral(ast::ExprStringLiteral { value, .. }) = elt {
                     if !acc.is_empty() {
-                        acc.push(',');
+                        acc.push_str(", ");
                     }
                     acc.push_str(value.to_str());
                 }