Remove Python 3.7 from zuul checks

It seems like nodes with Python 3.7 are no longer available
for testing on opendev.
et, leave Python 3.7 support in code.

Possibly, related announcement:
https://lists.opendev.org/archives/list/service-announce@lists.opendev.org/thread/EUTEAOIUQZ6YJUQWD75QO34H5TDGBLKP/

Also, add retry count for link checker.
This fixes transient http errors now occured at every job run.
May be, this was introduced by some zuul infrastructure changes.
Whithout this fix, no pipelines are able to run successfully.

Change-Id: I56fc90c742ee17d4486d4ec2042151207d5522e7

.zuul.yaml

@@ -23,7 +23,6 @@
 - project:
     templates:
       - docs-on-readthedocs
-      - openstack-python37-jobs-no-constraints
     vars:
       rtd_webhook_id: '47271'
     check:

doc/source/conf.py

@@ -229,6 +229,7 @@ latex_documents = [
 # If set, override pythons default socket timeout
 # testing has shown the default is too short so explicitly increase to 15 secs
 linkcheck_timeout = 15
+linkcheck_retries = 3
 
 
 # -- Options for manual page output ------------------------------------------

setup.cfg

@@ -22,8 +22,11 @@ classifier =
     Operating System :: OS Independent
     Programming Language :: Python
     Programming Language :: Python :: 3
-    Programming Language :: Python :: 3.7
     Programming Language :: Python :: 3.8
+    Programming Language :: Python :: 3.9
+    Programming Language :: Python :: 3.10
+    Programming Language :: Python :: 3.11
+    Programming Language :: Python :: 3.12
 
 [files]
 packages =