testsuite: add job-list database tests

Problem: There are no tests to cover the new job-list DB.

Add coverage in new t/t2263-job-list-db.t.

Author: chu11

t/Makefile.am

@@ -155,6 +155,7 @@ TESTSCRIPTS = \
 	t2260-job-list.t \
 	t2261-job-list-update.t \
 	t2262-job-list-stats.t \
+	t2263-job-list-db.t \
 	t2270-job-dependencies.t \
 	t2271-job-dependency-after.t \
 	t2272-job-begin-time.t \