chore: Updates after 3.1.0 release

[michalChrobot]

Purpose of this PR

PR that brings updates after 3.1.0 package release which are:

1. Usual changelog and package version update
2. ShadowPackage PR integrations (original PR was https://github.cds.internal.unity3d.com/unity/unity/pull/127141)
3. Update to automated release jobs as I spotted few issues

Jira ticket

N/A

Documentation

N/A

Testing & QA (How your changes can be verified during release Playtest)

Usual CI pass

Up-port

N/A

Backports

N/A

[u-pr]

⚠️ Some settings were ignored in '.pr_agent.toml (repository root)' repo settings

Check the configuration's TOML syntax, permitted settings, and size limit. See the error below.

---

Error message:
Ignored prohibited settings: github_app.handle_pr_actions. Permitted settings were applied.

Configuration content:

# This is the configuration for the u-pr bot
# https://github.cds.internal.unity3d.com/unity/u-pr
# For configuration of this file:
# https://developer.portal.internal.unity.com/catalog/default/component/u-pr/docs/configuration/automatic_runs/

[github_app]
handle_pr_actions = ['opened', 'ready_for_review']  # PR events that auto-run pr_commands
pr_commands       = ["/harness-review"]             # what runs on those events
reviewer_commands = ["/harness-review"]             # what runs when @u-pr is added as reviewer

[u-pr]

💡 Harness Review

The version and branch updates align with the release flow, and the Unity 7 scene callback is isolated; the changelog cleanup introduces a regression in release preparation.

_{Reviewed commit 1b42685}

_{🤖 Helpful? 👍/👎}

[codecov-github-com]

Codecov Report

All modified and coverable lines are covered by tests ✅

@@              Coverage Diff               @@
##           develop-3.x.x    #4183   +/-   ##
==============================================
  Coverage          78.19%   78.19%           
==============================================
  Files                153      153           
  Lines              26272    26272           
==============================================
  Hits               20544    20544           
  Misses              5728     5728           

Flag	Coverage Δ
NGOv2_project_testproject_ubuntu	76.65% <ø> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Components	Coverage Δ
com.unity.netcode.gameobjects	78.19% <ø> (ø)

ℹ️ Need help interpreting these results?

[NoelStephensUnity]

Thank you for this!

LGTM!