vtgate: fix race condition iterating tables and views from schema tra…

…cker (vitessio#13673)

go/vt/vtgate/schema/tracker.go

@@ -22,6 +22,8 @@ import (
 	"sync"
 	"time"
 
+	"golang.org/x/exp/maps"
+
 	"vitess.io/vitess/go/vt/discovery"
 	"vitess.io/vitess/go/vt/log"
 	querypb "vitess.io/vitess/go/vt/proto/query"
@@ -221,7 +223,7 @@ func (t *Tracker) Tables(ks string) map[string]*vindexes.TableInfo {
 		return map[string]*vindexes.TableInfo{} // we know nothing about this KS, so that is the info we can give out
 	}
 
-	return m
+	return maps.Clone(m)
 }
 
 // Views returns all known views in the keyspace with their definition.
@@ -232,7 +234,9 @@ func (t *Tracker) Views(ks string) map[string]sqlparser.SelectStatement {
 	if t.views == nil {
 		return nil
 	}
-	return t.views.m[ks]
+
+	m := t.views.m[ks]
+	return maps.Clone(m)
 }
 
 func (t *Tracker) updateSchema(th *discovery.TabletHealth) bool {