Description

cz bump --prerelease rc should handle missing "bumpable" commits the same way as cz bump.

Steps to reproduce

1. create a non-bumpable commit (i.e. ci or build)
2. run cz bump --prerelease rc --dry-run

Current behavior

The command terminates with an error:

$ cz bump --prerelease rc --dry-run
[NO_COMMITS_FOUND]
No commits found to generate a pre-release.
To avoid this error, manually specify the type of increment with `--increment`

Desired behavior

It should behave like running cz bump without --prerelease flag.

$ cz bump --dry-run 
bump: version 1.2.1 → 1.2.1 [skip ci]
tag to create: v1.2.1
increment detected: None

Environment

• commitizen version: 2.18.0
• python version: 3.9.4
• operating system: Darwin