Accept .py path-referenced packages in GitOps

[cdcme]

Related issue: Resolves #49370

fleetctl gitops rejected a local path:-referenced .py software package client-side with unsupported extension ".py", even though a url:-referenced .py worked end-to-end. The package-path switch and the two HydrateToPackageLevel gates (team-level advanced options + icon) only recognized .sh/.ps1. They now use fleet.IsScriptPackage, so .py is accepted — and future script types won't drift out of sync.

Checklist for submitter

• Changes file: N/A — unreleased fix on the #41470 feature branch; the feature PR (Allow Python script-only packages #49070) carries the changes file.
• Input data is properly validated (extension-gating fix only; no new input handling, SQL, or shell interpolation).

Testing

• Added/updated automated tests — TestScriptOnlyPackagesPathPy (path .py with team-level self-service, uninstall/post-install scripts, pre-install query, and icon); confirmed it fails without the fix and passes with it. Also updated a sibling test's error-string assertion.
• QA'd all new/changed functionality manually — live before/after with the real fleetctl binary: unfixed → unsupported extension ".py"; fixed → gitops dry run succeeded, and a real apply persisted the package with source: py_packages.