Disable 8.x DRA packaging from Jenkins (elastic#39387)

This commit disables triggering DRA packaging builds for the 8.x branch
via Jenkins.

Relates: elastic/ingest-dev#3095

---------

Co-authored-by: Victor Martinez <victormartinezrubio@gmail.com>

.ci/jobs/packaging.yml

@@ -14,7 +14,7 @@
           discover-pr-forks-trust: 'permission'
           discover-pr-origin: 'merge-current'
           discover-tags: true
-          head-filter-regex: '(7\.1[6789]|8\.13|PR-.*|v8\.13\.\d+)'
+          head-filter-regex: '(7\.17|PR-.*)'
           disable-pr-notifications: true
           notification-context: 'beats-packaging'
           repo: 'beats'
@@ -28,11 +28,8 @@
               ignore-tags-older-than: -1
               ignore-tags-newer-than: 30
           - named-branches:
-              - exact-name:
-                  name: '8.13'
-                  case-sensitive: true
               - regex-name:
-                  regex: '7\.1[6789]'
+                  regex: '7\.17'
                   case-sensitive: true
           - change-request:
               ignore-target-only-changes: true