Fix after-release and update CHANGELOG

[martincostello]

• Fix xpath to get the previous release veresion broken by Refactor project dependencies #2696.
• Update CHANGELOG and samples for v8.6.3.

[Copilot]

Pull Request Overview

This PR fixes a broken XPath selector in the version bumping script that was broken by a previous refactoring of project dependencies, and updates the changelog and version to reflect the new v8.6.3 release.

• Updates XPath selector to correctly locate package version in the new file structure
• Updates package version from 8.6.2 to 8.6.3
• Adds changelog entries for v8.6.3 release

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
eng/bump-version.ps1	Fixes XPath selector to match new package structure and updates property access
Directory.Packages.props	Bumps Polly package version to 8.6.3
CHANGELOG.md	Adds release notes for v8.6.3 with list of included changes

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.12%. Comparing base (cf50bc5) to head (dd1b0d4).
⚠️ Report is 2 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2714   +/-   ##
=======================================
  Coverage   96.12%   96.12%           
=======================================
  Files         309      309           
  Lines        7118     7118           
  Branches     1006     1006           
=======================================
  Hits         6842     6842           
  Misses        222      222           
  Partials       54       54           

Flag	Coverage Δ
linux	96.12% <ø> (ø)
macos	96.12% <ø> (ø)
windows	96.11% <ø> (ø)

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