Prioritize "bug" label for changelog sections (#16433)

## Summary

This PR updates the ordering of changelog sections to prioritize `bug`
label such that any PRs that has that label is categorized in "Bug
fixes" section in when generating the changelog irrespective of any
other labels present on the PR.

I think this works because I've seen PRs with both `server` and `bug` in
the "Server" section instead of the "Bug fixes" section. For example,
https://github.com/astral-sh/ruff/pull/16262 in
https://github.com/astral-sh/ruff/releases/tag/0.9.7.

On that note, this also changes the ordering such that any PR with both
`server` and `bug` labels are in the "Bug fixes" section instead of the
"Server" section. This is in line with how "Formatter" is done. I think
it makes sense to instead prefix the entries with "Formatter:" and
"Server:" if they're bug fixes. But, I'm happy to change this such that
any PRs with `formatter` and `server` labels are always in their own
section irrespective of other labels.

pyproject.toml

@@ -113,17 +113,17 @@ changelog_ignore_labels = ["internal", "ci", "red-knot", "testing"]
 
 changelog_sections.breaking = "Breaking changes"
 changelog_sections.preview = "Preview features"
+changelog_sections.bug = "Bug fixes"
 changelog_sections.rule = "Rule changes"
 changelog_sections.diagnostics = "Rule changes"
 changelog_sections.docstring = "Rule changes"
 changelog_sections.fixes = "Rule changes"
-changelog_sections.formatter = "Formatter"
 changelog_sections.isort = "Rule changes"
 changelog_sections.performance = "Performance"
+changelog_sections.formatter = "Formatter"
 changelog_sections.server = "Server"
 changelog_sections.cli = "CLI"
 changelog_sections.configuration = "Configuration"
-changelog_sections.bug = "Bug fixes"
 changelog_sections.documentation = "Documentation"
 changelog_sections.__unknown__ = "Other changes"