test: add table_synonyms to list of expected tables (GoogleCloudPlatform#3813)

Spanner now has a table_synonyms table in information_schema.

Author: olavloite

.ci/e2e-expected/backslash-dt.txt

@@ -39,6 +39,7 @@
  testdb_e2e_psql_v?? | information_schema | spanner_statistics               | VIEW       |                              |                      |                           |                          |                        |                    |          |               |                   |                  |               |                 |
  testdb_e2e_psql_v?? | information_schema | table_constraints                | VIEW       |                              |                      |                           |                          |                        |                    |          |               |                   |                  |               |                 |
  testdb_e2e_psql_v?? | information_schema | table_privileges                 | VIEW       |                              |                      |                           |                          |                        |                    |          |               |                   |                  |               |                 |
+ testdb_e2e_psql_v?? | information_schema | table_synonyms                   | VIEW       |                              |                      |                           |                          |                        |                    |          |               |                   |                  |               |                 |
  testdb_e2e_psql_v?? | information_schema | tables                           | VIEW       |                              |                      |                           |                          |                        |                    |          |               |                   |                  |               |                 |
  testdb_e2e_psql_v?? | information_schema | views                            | VIEW       |                              |                      |                           |                          |                        |                    |          |               |                   |                  |               |                 |
  testdb_e2e_psql_v?? | spanner_sys        | active_partitioned_dmls          | VIEW       |                              |                      |                           |                          |                        |                    |          |               |                   |                  |               |                 |
@@ -87,5 +88,5 @@
  testdb_e2e_psql_v?? | spanner_sys        | txn_stats_total_hour             | VIEW       |                              |                      |                           |                          |                        |                    |          |               |                   |                  |               |                 | 
  testdb_e2e_psql_v?? | spanner_sys        | txn_stats_total_minute           | VIEW       |                              |                      |                           |                          |                        |                    |          |               |                   |                  |               |                 | 
  testdb_e2e_psql_v?? | spanner_sys        | user_split_points                | VIEW       |                              |                      |                           |                          |                        |                    |          |               |                   |                  |               |                 | 
-(86 rows)
+(87 rows)