t1011: update comment above test

Problem: One of the tests in t1011-job-archive-interface.t has a
lengthy comment explaining in more detail what is being checked in the
test itself, but it is missing an important "not" when describing the
effect on the job usage value for an association.

Fix this comment by adding a "not" to the sentence.

t/t1011-job-archive-interface.t

@@ -139,7 +139,7 @@ test_expect_success 'check that job usage and fairshare values get updated' '
 '
 
 # if update-usage is called in the same half-life period when no jobs are found
-# for a user, their job usage factor should be affected; this test is taken
+# for a user, their job usage factor should not be affected; this test is taken
 # from the set of job-archive interface Python unit tests
 test_expect_success 'call update-usage in the same half-life period where no jobs are run' '
 	flux account -p ${DB_PATH} update-usage &&