kvserver: unskip the thresholdFirst=true variants of `TestGCThresho…

…ldRacesWithRead`

This commit unskips a subset of `TestGCThresholdRacesWithRead`, which is now
possible because of cockroachdb#76312 and the first commit in this patch. See
cockroachdb#76410 (comment)

Relates to cockroachdb#55293.

Release note: none

pkg/kv/kvserver/replica_test.go

@@ -8572,7 +8572,6 @@ func TestRefreshFromBelowGCThreshold(t *testing.T) {
 func TestGCThresholdRacesWithRead(t *testing.T) {
 	defer leaktest.AfterTest(t)()
 	defer log.Scope(t).Close(t)
-	skip.WithIssue(t, 55293)
 
 	testutils.RunTrueAndFalse(t, "followerRead", func(t *testing.T, followerRead bool) {
 		testutils.RunTrueAndFalse(t, "thresholdFirst", func(t *testing.T, thresholdFirst bool) {