📝 Improve changelog and upgrade guide (#450)

## Description

This PR improves the changelog and upgrade guide with regard to the
discontinuation of x86 macOS support. Support was initially dropped in
#421. See munich-quantum-toolkit/core#1165 for
more information.

Fixes #432

## Checklist:

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This checklist serves as a reminder of a couple of things that ensure
your pull request will be merged swiftly.
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- [x] The pull request only contains commits that are focused and
relevant to this change.
- [x] ~I have added appropriate tests that cover the new/changed
functionality.~
- [x] ~I have updated the documentation to reflect these changes.~
- [x] I have added entries to the changelog for any noteworthy
additions, changes, fixes, or removals.
- [x] I have added migration instructions to the upgrade guide (if
needed).
- [x] The changes follow the project's style guidelines and introduce no
new warnings.
- [x] The changes are fully tested and pass the CI checks.
- [x] I have reviewed my own code changes.

Author: denialhaag

CHANGELOG.md

@@ -9,6 +9,10 @@ This project adheres to [Semantic Versioning], with the exception that minor rel
 
 ## [Unreleased]
 
+### Changed
+
+- 🔥 Drop support for x86 macOS systems ([#421]) ([**@denialhaag**])
+
 ## [2.3.0] - 2025-07-29
 
 _If you are upgrading: please see [`UPGRADING.md`](UPGRADING.md#230)._
@@ -20,7 +24,6 @@ _If you are upgrading: please see [`UPGRADING.md`](UPGRADING.md#230)._
 
 ### Changed
 
-- 🗑️ Drop support for x86 architecture on macOS ([#421]) ([**@denialhaag**])
 - 🎨 Adjust the ESP reward calculation to become Qiskit v2 compatible ([#406]) ([**@nquetschlich**])
 - ✨ Improve the ML part and its usability ([#403]) ([**@nquetschlich**])
 - 📝 Migrate the documentation from .rst to .md files ([#403]) ([**@nquetschlich**])
@@ -40,7 +43,7 @@ _📚 Refer to the [GitHub Release Notes](https://github.com/munich-quantum-tool
 
 <!-- PR links -->
 
-[#421]: https://github.com/munich-quantum-toolkit/predictor/pull/406
+[#421]: https://github.com/munich-quantum-toolkit/predictor/pull/421
 [#406]: https://github.com/munich-quantum-toolkit/predictor/pull/406
 [#405]: https://github.com/munich-quantum-toolkit/predictor/pull/405
 [#403]: https://github.com/munich-quantum-toolkit/predictor/pull/403

UPGRADING.md

@@ -4,8 +4,12 @@ This document describes breaking changes and how to upgrade. For a complete list
 
 ## [Unreleased]
 
-With this release, `mqt-predictor` no longer supports the x86 architecture on macOS.
-This step was necessary to ensure compatibility with PyTorch.
+### End of support for x86 macOS systems
+
+Starting with this release, MQT Predictor no longer supports x86 macOS systems.
+This step is necessary to ensure compatibility with PyTorch.
+Furthermore, this coincides with GitHub removing the `macos-13` runners from their infrastructure.
+x86 macOS systems are no longer tested in our CI.
 
 ## [2.3.0] - 2025-07-29
 
@@ -19,7 +23,7 @@ The RL action handling has been updated to utilize dataclasses, which improves t
 
 ### General
 
-MQT Bench has moved to the [munich-quantum-toolkit](https://github.com/munich-quantum-toolkit) GitHub organization under https://github.com/munich-quantum-toolkit/predictor.
+MQT Predictor has moved to the [munich-quantum-toolkit](https://github.com/munich-quantum-toolkit) GitHub organization under https://github.com/munich-quantum-toolkit/predictor.
 While most links should be automatically redirected, please update any links in your code to point to the new location.
 All links in the documentation have been updated accordingly.