Fix broken test caused by setting old write index to read-only verifi…

…ed (#123190) (#123209)

#122887 set read-only on the source indices of a data stream reindex. To test behavior when the source index was already read-only, testDataStreamUpgrade sometimes set the old write index to read-only. But the rest end point for adding a read-only block always sets verifed-read-only. This caused the old write index to not need to be upgraded, resulting in an incorrect value for total_indices_requiring_upgrade

(cherry picked from commit 8b25a72)

# Conflicts:
#	muted-tests.yml

x-pack/qa/rolling-upgrade/src/test/java/org/elasticsearch/upgrades/DataStreamsUpgradeIT.java

@@ -566,9 +566,6 @@ private void upgradeDataStream(String dataStreamName, int numRolloversOnOldClust
             if (randomBoolean()) {
                 closeIndex(oldIndexName);
             }
-            if (randomBoolean()) {
-                assertOK(client().performRequest(new Request("PUT", oldIndexName + "/_block/read_only")));
-            }
         }
         Request reindexRequest = new Request("POST", "/_migration/reindex");
         reindexRequest.setJsonEntity(Strings.format("""