Fix store debug matchers panic on regex matcher

[x] I added CHANGELOG entry for this change.
[ ] Change is not relevant to the end user.

Changes

Fixes https://github.com/thanos-io/thanos/issues/7676

ParseMetricSelector tries to copy label matchers but there is a new field re for the underlying regex and it is not copied, causing panic when calling Matches.

    for i, lm := range vs.LabelMatchers {
        matchers[i] = &labels.Matcher{
            Type:  lm.Type,
            Name:  lm.Name,
            Value: lm.Value,
        }
    }

Verification

Added a simple unit test. Without the change in this PR the test will panic when calling Matches.

thanos-io / thanos

Fix store debug matchers panic on regex matcher #7903

Changes

Verification