fix yum proxy regex (closes #47797) (#47800)

* Modify yum/tasks/proxy.yml to usernames that expose regex bug

* Fix bad regex backref/interpolation w/yum proxy username

A yum proxy username that begins with a number was being
interpolated as part of the backref, resulting in an error:
"sre_constants.error: invalid group reference"

Closes #47797

lib/ansible/modules/packaging/os/yum.py

@@ -710,7 +710,7 @@ class YumModule(YumDnf):
                     for item in scheme:
                         os.environ[item + "_proxy"] = re.sub(
                             r"(http://)",
-                            r"\1" + namepass, proxy_url
+                            r"\g<1>" + namepass, proxy_url
                         )
             yield
         except yum.Errors.YumBaseError: