CI: Pin ansible-lint to <6

The molecule job is failing with the following since the release of
ansible-lint 6.0.0:

    ModuleNotFoundError: No module named 'ansiblelint.prerun'

Pin ansible-lint to <6.

Also ignore changes to molecule-requirements.txt for jobs that don't use
it.

Change-Id: I00ea1b4cd57a22a1a0939ddc463ef336da2f0902

molecule-requirements.txt

@@ -2,6 +2,7 @@
 # of appearance. Changing the order has an impact on the overall integration
 # process, which may cause wedges in the gate later.
 
+ansible-lint>=3.0.0,<6.0.0,!=4.3.0 # MIT
 docker # Apache-2.0
 molecule<3.5.0 # MIT
 molecule-docker # MIT

zuul.d/jobs.yaml

@@ -9,6 +9,7 @@
     irrelevant-files:
       - ^.*\.rst$
       - ^doc/.*
+      - ^molecule-requirements.txt
       - ^releasenotes/.*
       - ^setup.cfg$
       - ^zuul.d/.*
@@ -25,6 +26,7 @@
     irrelevant-files:
       - ^.*\.rst$
       - ^doc/.*
+      - ^molecule-requirements.txt
       - ^releasenotes/.*
       - ^setup.cfg$
       - ^zuul.d/.*
@@ -66,6 +68,7 @@
     irrelevant-files:
       - ^.*\.rst$
       - ^doc/.*
+      - ^molecule-requirements.txt
       - ^releasenotes/.*
       - ^setup.cfg$
       - ^test-requirements.txt