Stabilize output of new regression test.

Commit 48c5c9068 failed to allow for buildfarm animals that
force jit = on.  I'm surprised that this hasn't come up
elsewhere in explain.sql, so turn it off for that whole
test script not just the one new test case.

Per buildfarm.

src/test/regress/expected/explain.out

@@ -47,6 +47,9 @@ begin
     return data::jsonb;
 end;
 $$;
+-- Also, disable JIT, or we'll get different output on machines
+-- where that's been forced on
+set jit = off;
 -- Simple cases
 select explain_filter('explain select * from int8_tbl i8');
                      explain_filter                      

src/test/regress/sql/explain.sql

@@ -51,6 +51,11 @@ begin
 end;
 $$;
 
+-- Also, disable JIT, or we'll get different output on machines
+-- where that's been forced on
+set jit = off;
+
+
 -- Simple cases
 
 select explain_filter('explain select * from int8_tbl i8');