[BACKPORT 2.8][#7376] YSQL: partial fix test insertsWhileCreatingIndex

Summary:
Java test TestIndexBackfill#insertsWhileCreatingIndex fails for two
reasons:

- some transient failure messages are not caught/allowed
- index state changes may not properly wait

Fix the first cause: add more messages that are allowed.  This should
reduce the test flakiness but not fully fix it.

Leave issue #7376 open.

Original commit: 90fa310 / D20329

Test Plan:
Jenkins: test regex: .*TestIndexBackfill#insertsWhileCreatingIndex

Ensure the following only fails with "Mismatch at row" errors (which are
for the index state change issue):

    ./yb_build.sh fastdebug --gcc11 \
      --java-test 'org.yb.pgsql.TestIndexBackfill#insertsWhileCreatingIndex' \
      -n 1000 --tp 1

Reviewers: alex

Reviewed By: alex

Differential Revision: https://phabricator.dev.yugabyte.com/D20637

java/yb-pgsql/src/test/java/org/yb/pgsql/TestIndexBackfill.java

@@ -218,6 +218,10 @@ private boolean isIgnorableException(Exception ex) {
     String msgLc = ex.getMessage().toLowerCase();
     return msgLc.contains("schema version mismatch")
         || msgLc.contains("catalog version mismatch")
-        || (msgLc.contains("resource unavailable") && msgLc.contains("rocksdb"));
+        || (msgLc.contains("resource unavailable") && (msgLc.contains("rocksdb")
+                                                       || msgLc.contains("null")))
+        || msgLc.contains("expired or aborted by a conflict")
+        || msgLc.contains("operation expired: transaction aborted:")
+        || msgLc.contains("transaction was recently aborted");
   }
 }