Fix flaky couch_jobs tests

[nickva]

Recently we fixed some of the flaky couch_jobs tests: #3414

However there seem to be others. This is an issue to keep track of them so we don't forget them:

(Thanks to @bessbd for discovering and reporting these)

      couch_jobs_tests:42: couch_jobs_basic_test_ (type_timeouts_and_server)...*failed*
in function couch_jobs_tests:'-type_timeouts_and_server/1-fun-9-'/0 (test/couch_jobs_tests.erl, line 235)
in call from couch_jobs_tests:type_timeouts_and_server/1 (test/couch_jobs_tests.erl, line 234)
**error:{assertEqual,[{module,couch_jobs_tests},
              {line,235},
              {expression,"length ( couch_jobs_activity_monitor_sup : get_child_pids ( ) )"},
              {expected,3},
              {value,4}]}
  output:<<"">>

in call from eunit_proc:run_group/2 (eunit_proc.erl, line 549)
**error:{badmatch,[<0.1005.0>,<0.1008.0>,<0.1012.0>]}
  output:<<"">>

in call from eunit_proc:run_group/2 (eunit_proc.erl, line 549)
**error:{badmatch,[<0.1546.0>,<0.1550.0>,<0.1543.0>]}
  output:<<"">>

      couch_jobs_tests:71: couch_jobs_basic_test_ (check_get_jobs)...*failed*
in function couch_jobs_tests:'-check_get_jobs/1-fun-0-'/4 (test/couch_jobs_tests.erl, line 645)
in call from couch_jobs_tests:check_get_jobs/1 (test/couch_jobs_tests.erl, line 642)
**error:{assertMatch,[{module,couch_jobs_tests},
              {line,645},
              {expression,"lists : sort ( couch_jobs_fdb : get_jobs ( ) )"},
              {pattern,"[ { T2 , J2 , pending , # { } } , { T1 , J1 , pending , # { } } ]"},
              {value,[{42,<<"j2">>,pending,#{}},
                      {{<<"t1">>,1024},<<"j1">>,pending,#{}},
                      {<<"db_expiration">>,<<"db_expiration_job-"...>>,
                       pending,#{}}]}]}
  output:<<"">>

     couch_jobs_tests:73: couch_jobs_basic_test_ (metadata_version_bump)...*failed*
in function couch_jobs_tests:'-metadata_version_bump/1-fun-3-'/1 (test/couch_jobs_tests.erl, line 677)
in call from couch_jobs_tests:metadata_version_bump/1 (test/couch_jobs_tests.erl, line 677)
in call from eunit_test:run_testfun/1 (eunit_test.erl, line 71)
in call from eunit_proc:run_test/1 (eunit_proc.erl, line 510)
in call from eunit_proc:with_timeout/3 (eunit_proc.erl, line 335)
in call from eunit_proc:handle_test/2 (eunit_proc.erl, line 493)
in call from eunit_proc:tests_inorder/3 (eunit_proc.erl, line 435)
in call from eunit_proc:with_timeout/3 (eunit_proc.erl, line 325)
**error:{assertMatch,
    [{module,couch_jobs_tests},
     {line,677},
     {expression,"JTx2"},
     {pattern,"# { md_version := Bin } when is_binary ( Bin )"},
     {value,
         #{jobs_path => <<21,52,21,51>>,
           jtx => true,
           layer_prefix => <<21,52>>,
           md_version => not_found,
           tx => {erlfdb_transaction,#Ref<0.3514692526.3705798658.247401>}}}]}
  output:<<"">>