Bump to version: v4.27.0

[zhikaip]

Version bump

This issue is a tracker issue for bumping PhysLean to new versions of Lean.
The checklist below should be used to ensure that the bump is done correctly.

Basics

• Update mathlib rev in lakefile.toml.
• Update doc-gen4 rev in lakefile.toml.
• Run rm -rf .lake; lake update.
• Check lean-toolchain updates correctly.
• Update the Lean version badge in the README.md file.

Build

• Run lake build and fix any errors.

Scripts

• Ensure lake exe lint_all runs without errors.
• Ensure lake exe TODO_to_yml mkFile runs without errors.
• Ensure lake exe stats mkHTML runs without errors.
• Ensure lake exe informal mkFile mkDot mkHTML runs without errors.
• Ensure lake exe make_tag runs without errors.
• Remove the created files rm ./docs/Informal.md; rm ./docs/InformalDot.dot; rm ./docs/InformalGraph.html; rm ./docs/Stats.html; rm ./docs/_data/TODO.yml.

Afterwards

• Create a tag for the new version.

Previous bump

v4.26.0

[zhikaip]

completed in #929