sql: stop swallowing errors from UncachedPhysicalAccessor.IsValidSchema

Before this commit we'd swallow retriable errors during execution. This can
be very problematic as it can lead to lost writes and other general funkiness.
We're opting to not write a test for this specific case as there is ongoing
work to change interfaces to preclude this sort of bug.

Fixes #43067
Fixes #37883 (comment)

Release note: None

pkg/sql/physical_schema_accessors.go

@@ -102,7 +102,10 @@ func (a UncachedPhysicalAccessor) GetObjectNames(
 	flags tree.DatabaseListFlags,
 ) (TableNames, error) {
 	ok, schemaID, err := a.IsValidSchema(ctx, txn, dbDesc.ID, scName)
-	if !ok || err != nil {
+	if err != nil {
+		return nil, err
+	}
+	if !ok {
 		if flags.Required {
 			tn := tree.MakeTableNameWithSchema(tree.Name(dbDesc.Name), tree.Name(scName), "")
 			return nil, sqlbase.NewUnsupportedSchemaUsageError(tree.ErrString(&tn.TableNamePrefix))