fix(manager/pre-commit): allow leading zeros in semver-coerced versioning for CalVer support

[vivodi]

Changes

Make semver-coerced versioning more permissive by allowing leading zeros, i.e. supporting calendar versioning.

pre-commit.ci bot can update Calendar Versioning dependencies (e.g. 2026.08.01 → 2026.08.08), but Renovate currently errors on such dependencies:

DEBUG: Dependency henryiii/validate-pyproject-schema-store has unsupported/unversioned value 2026.08.01 (versioning=semver-coerced)

This PR makes Renovate behave like the pre-commit.ci bot, allowing it to correctly update dependencies with leading zeros.

Context

Please select one of the following:

• This closes an existing Issue, Closes: pre-commit: semver-coerced fails to parse CalVer tags with leading zeros (e.g., 2025.08.07) #39894
• This doesn't close an Issue, but I accept the risk that this PR may be closed if maintainers disagree with its opening or implementation

AI assistance disclosure

Did you use AI tools to create any part of this pull request?

Please select one option and, if yes, briefly describe how AI was used (e.g., code, tests, docs) and which tool(s) you used.

• No — I did not use AI for this contribution.
• Yes — minimal assistance (e.g., IDE autocomplete, small code completions, grammar fixes).
• Yes — substantive assistance (AI-generated non‑trivial portions of code, tests, or documentation).
• Yes — other (please describe):

Use of AI in replying to PR comments

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Documentation (please check one with an [x])

• I have updated the documentation, or
• No documentation update is required

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I have verified these changes via:

• Code inspection only, or
• Newly added/modified unit tests, or
• No unit tests, but ran on a real repository, or
• Both unit tests + ran on a real repository

The public repository: https://github.com/vivodi/loose-semver-coerced