Improvements for release_process.md (#4756)

* Improvements for release_process.md

While cutting 25.9.0, I ran into a few snags, so this PR smooths out the issues I ran into in the docs:

- Minor typo fix
- Since the stable branch is updated by the release workflow, `git diff origin/stable CHANGES.md` should always work, which is much easier than having to find a commit hash
- The example PR given had the new template already applied, which confused me. I eventually used the 25.1.0 pr as a template instead
- GitHub appears to now use the last commit message as the release message instead of the tag name, so it will need to be entered manually going forwards

* Update release_process.md

There is now a check to prevent any direct pushes to main, so a PR has to be made

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci



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Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>