Fix AsciiDoc rendering of path variable regex examples

[hallykeeg]

This PR fixes the issue #35378

[bclozel]

@hallykeeg thanks for raising this PR.
Could you also fix the same issue in the WebFlux section please?

Note that we cannot merge your contribution until you have signed the DCO. For that, you can use the following commands:

# update the webflux section
git add .
git amend -s
git push --force