Fix the example for blank-line-before-class (D211) (#5746)
The example for
[D211](https://beta.ruff.rs/docs/rules/blank-line-before-class/) is
currently identical to the example for
[D203](https://beta.ruff.rs/docs/rules/one-blank-line-before-class/). It
should be the opposite, with the incorrect case having a blank line
before the class docstring and the correct case having no blank line.
