dev-cmd/bump: check if Repology output is a version first

[dawidd6]

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Follow-up to: #14190

Before:

Mon 05 Dec 16:16:05 ➜  Library/Homebrew stash master ✓  brew bump cortex --open-pr
==> cortex
Current formula version:  1.13.1
Latest livecheck version: 1.14.0
Latest Repology version:  present only in Homebrew
Open pull requests:       cortex 1.14.0 (https://github.com/Homebrew/homebrew-core/pull/117195)
cortex was not bumped to the Repology version because it's livecheckable.

After:

Mon 05 Dec 16:16:19 ➜  Library/Homebrew master ✗  brew bump cortex --open-pr
==> cortex
Current formula version:  1.13.1
Latest livecheck version: 1.14.0
Latest Repology version:  present only in Homebrew
Open pull requests:       cortex 1.14.0 (https://github.com/Homebrew/homebrew-core/pull/117195)

Basically the output about "not bumping because livecheckable" should not happen in the case software is unique to Homebrew.

[BrewTestBot]

Review period will end on 2022-12-06 at 15:22:59 UTC.

[BrewTestBot]

Review period ended.