Previously we were using the "semver" library to parse version
constraints, but we switched over to go-version and encapsulated it
inside our own plugin/discovery package to reduce dependency sprawl in
the code.
This particular situation was missed when updating references to the new
path, which meant that our validation code disagreed with the rest of
the code about what is considered a valid version constraint string.
By using the correct function, we ensure that we catch early any invalid
versions.
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