Bump Jenkins version to 2.426.3

[michael-doubez]

Based on version extract, it seems safe to bump Jenkins version to 2.426.3. At the same time, update JCasc as indictated in #327

Also prepare for jetty 12 as requested in JENKINS-73141

Submitter checklist

• [X] Make sure you are opening from a topic/feature/bugfix branch (right side) and not your main branch!
• [X] Ensure that the pull request title represents the desired changelog entry
• [X] Please describe what you did
• [X] Link to relevant issues in GitHub or Jira
• [X] Link to relevant pull requests, esp. upstream and downstream changes

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 73.59%. Comparing base (bca3705) to head (31c64a9). Report is 10 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #346 +/- ## ============================================ + Coverage 72.46% 73.59% +1.12% - Complexity 201 209 +8 ============================================ Files 9 10 +1 Lines 839 852 +13 Branches 119 120 +1 ============================================ + Hits 608 627 +19 + Misses 170 163 -7 - Partials 61 62 +1 ```

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