Remove unused cross-arch files and docs

.github/RELEASE_NOTES.template.md

@@ -13,7 +13,7 @@
 All upgrading should be done via the migration script or regenerating the templates.
 
 ```bash
-curl -sSL https://raw.githubusercontent.com/frequenz-floss/frequenz-repo-config-python/<tag>/cookiecutter/migrate.py | python3
+curl -sSLf https://raw.githubusercontent.com/frequenz-floss/frequenz-repo-config-python/<tag>/cookiecutter/migrate.py | python3 -I
 ```
 
 But you might still need to adapt your code:

.github/cookiecutter-migrate.template.py

@@ -21,7 +21,7 @@
 """  # noqa: E501
 
 # R0801 is similarity detection, as the template is always similar to the current script
-# pylint: disable=too-many-lines, too-many-locals, too-many-branches, R0801
+# pylint: disable=too-many-lines, too-many-locals, too-many-branches, too-many-statements, R0801
 
 import hashlib
 import json

CONTRIBUTING.md

@@ -261,30 +261,3 @@ These are the steps to create a new release:
    should be automated eventually too).
 
 7. Celebrate!
-
-##  Cross-Arch Testing
-
-This project has built-in support for testing across multiple architectures.
-Currently, our CI conducts tests on `arm64` machines using QEMU emulation. We
-also have the flexibility to expand this support to include additional
-architectures in the future.
-
-This project contains Dockerfiles that can be used in the CI to test the
-python package in non-native machine architectures, e.g., `arm64`. The
-Dockerfiles exist in the directory `.github/containers/nox-cross-arch`, and
-follow a naming scheme so that they can be easily used in build matrices in the
-CI, in `nox-cross-arch` job. The naming scheme is:
-
-```
-<arch>-<os>-python-<python-version>.Dockerfile
-```
-
-E.g.,
-
-```
-arm64-ubuntu-20.04-python-3.11.Dockerfile
-```
-
-If a Dockerfile for your desired target architecture, OS, and python version
-does not exist here, please add one before proceeding to add your options to
-the test matrix.

RELEASE_NOTES.md

@@ -2,10 +2,12 @@
 
 ## Summary
 
-This release improves workflows security, adds a black migration workflow, and fixes failed migrations from version v0.16.0.
+<!-- Here goes a general summary of what this release is about -->
 
 ## Upgrading
 
+<!-- Here goes notes on how to upgrade from previous versions, including deprecations and what they should be replaced with -->
+
 ### Cookiecutter template
 
 All upgrading should be done via the migration script or regenerating the templates.
@@ -16,16 +18,20 @@ curl -sSLf https://raw.githubusercontent.com/frequenz-floss/frequenz-repo-config
 
 But you might still need to adapt your code:
 
+<!-- Here upgrade steps for cookiecutter specifically -->
+
 ## New Features
 
+<!-- Here goes the main new features and examples or instructions on how to use them -->
+
 ### Cookiecutter template
 
-- Add a `black-migration.yaml` workflow that automatically reformats code when Dependabot upgrades `black`.
+<!-- Here new features for cookiecutter specifically -->
 
 ## Bug Fixes
 
+<!-- Here goes notable bug fixes that are worth a special mention or explanation -->
+
 ### Cookiecutter template
 
-- Fix migration of CI workflow matrices that used `arch`/`os` dimensions with values different from the default template. The v0.16.0 migration relied on exact string matching, so projects with customized matrix items (for example `arch: [amd64]`, `os: [ubuntu-24.04]`) could be left only partially migrated. The new migration step rebuilds the `platform` entries from the existing `arch`/`os` values and only rewrites `runs-on` when it still points to the old matrix keys.
-- Improve workflows security: tighten permissions, avoid potential shell injection, run Python in isolated mode, pin all dependencies using the SHA hash.
 - The unused cross-arch QEMU-based testing infrastructure has been removed. The `.github/containers/nox-cross-arch/` and `.github/containers/test-installation/` directories, as well as the "Cross-Arch Testing" section in `CONTRIBUTING.md`.