Ruby dependencies should only be invoked when the legacy flag is passed

[karreiro]

WHY are these changes introduced?

Ruby dependencies should only be invoked when the legacy flag is passed. However, users receive the following message when they try to invoke shopify theme dev.

WHAT is this pull request doing?

When the --legacy flag is not passed, it defaults to undefined, and then the mechanism that refreshes the session is invoked. This regression was introduced after the dev preview when we inverted the logic from --dev-preview to --legacy.

How to test your changes?

• Run shopify theme dev

Post-release steps

N/A

Measuring impact

How do we know this change was effective? Please choose one:

• n/a - this doesn't need measurement, e.g. a linting rule or a bug-fix
• Existing analytics will cater for this addition
• PR includes analytics changes to measure impact

Checklist

• I've considered possible cross-platform impacts (Mac, Linux, Windows)
• I've considered possible documentation changes

[github-actions]

We detected some changes at either packages/*/src or packages/cli-kit/assets/cli-ruby/** and there are no updates in the .changeset.
If the changes are user-facing, run "pnpm changeset add" to track your changes and include them in the next release CHANGELOG.

[github-actions]

Coverage report

St.❔	Category	Percentage	Covered / Total
🟡	Statements	73% (+0.01% 🔼)	8389/11491
🟡	Branches	69.56% (+0.02% 🔼)	4091/5881
🟡	Functions	71.75%	2179/3037
🟡	Lines	73.35% (+0.01% 🔼)	7938/10822

Test suite run success

1889 tests passing in 857 suites.

Report generated by 🧪jest coverage report action from e41f21f