ci: freebsd: Specify debug_parallel_query=regress

A lot of buildfarm animals run with debug_parallel_query=regress, while CI
didn't test that. That lead to the annoying situation of only noticing related
test instabilities after merging changes upstream.

FreeBSD was chosen because it's a relatively fast task. It also tests
debug_write_read_parse_plan_trees etc, which probably is exercised a bit more
heavily with debug_parallel_query=regress.

Discussion: https://postgr.es/m/zbuk4mlov22yfoktf5ub3lwjw2b7ezwphwolbplthepda42int@h6wpvq7orc44

Author: anarazel

.cirrus.tasks.yml

@@ -139,7 +139,14 @@ task:
     CPPFLAGS: -DRELCACHE_FORCE_RELEASE -DENFORCE_REGRESSION_TEST_NAME_RESTRICTIONS
     CFLAGS: -Og -ggdb
 
-    PG_TEST_INITDB_EXTRA_OPTS: -c debug_copy_parse_plan_trees=on -c debug_write_read_parse_plan_trees=on -c debug_raw_expression_coverage_test=on
+    # Several buildfarm animals enable these options. Without testing them
+    # during CI, it would be easy to cause breakage on the buildfarm with CI
+    # passing.
+    PG_TEST_INITDB_EXTRA_OPTS: >-
+      -c debug_copy_parse_plan_trees=on
+      -c debug_write_read_parse_plan_trees=on
+      -c debug_raw_expression_coverage_test=on
+      -c debug_parallel_query=regress
     PG_TEST_PG_UPGRADE_MODE: --link
 
   <<: *freebsd_task_template