fix: set version task

[Diaphteiros]

What this PR does / why we need it:
During a release of the openmcp-operator, the lines

replace (
	github.com/openmcp-project/openmcp-operator/api => ./api
	github.com/openmcp-project/openmcp-operator/lib => ./lib
)

got replaced with

replace (
	github.com/openmcp-project/openmcp-operator/api <new_version>
	github.com/openmcp-project/openmcp-operator/lib <new_version>
)

This was due to a wrong regex, which was not expected to match these lines.

The problem didn't occur in the past and also not in other projects, because there we always have only a single replace statement, not a block, and the line needs to start with whitespace to be matched.

I added a v in the regex, so that it will now only match lines that have a version after the module path.

Which issue(s) this PR fixes:
None

Special notes for your reviewer:

Release note:

The `release:set-version` task had a bug that caused it to replace some lines in the `go.mod` file that it wasn't supposed to replace. This is now fixed.