Refine VCS URL install error message wording in Transaction.add_requirement - #278

Create a follow-up pull request in pyodide/micropip that addresses the remaining review comments left on merged PR #277 ("Raise a helpful error for VCS URLs in install()").

Context:

• PR Raise a helpful error for VCS URLs in install() #277 was merged into main on 2026-05-20.
• The PR added a helpful ValueError for VCS URLs in Transaction.add_requirement, tests in tests/test_transaction.py, and a changelog entry.
• After merge, a reviewer noted there was still one nit/comment worth applying in a follow-up PR.

Relevant review feedback to address:

1. In micropip/transaction.py, reviewer agriyakhetarpal suggested reflowing the error message formatting for cleanliness. The intended updated code is:

        if isinstance(req, str) and _looks_like_vcs_url(req):
            raise ValueError(
                f"Cannot install {req!r}: micropip only installs prebuilt wheels "
                "and does not support installing from a VCS URL "
                "(git+, hg+, svn+, bzr+). Provide a URL pointing to a wheel "
                "or a package name available on a configured index."
            )

Notes:

• The current merged code says: Provide a wheel URL or a package name available on a configured index.
• The requested follow-up wording is: Provide a URL pointing to a wheel or a package name available on a configured index.
• Preserve the surrounding logic and existing helper _looks_like_vcs_url unless additional cleanup is clearly beneficial.
• Update or add tests only if needed to keep coverage correct.

Please create a PR with just the necessary changes to address that feedback cleanly and minimally.

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