fix: ignore an injected WebSession parameter

[kdelay]

WebSession is injected by WebFlux without an annotation, but the WebFlux RequestService ignore list only holds ServerWebExchange, ServerHttpRequest, ServerHttpResponse and ServerRequest. A handler that asks for one gets it documented:

{"name":"session","in":"query","required":true,"schema":{"$ref":"#/components/schemas/WebSession"}}

with components.schemas.WebSession holding the whole interface (id, attributes, creationTime, expired, lastAccessTime, maxIdleTime, started). Same shape as #3317.

This adds WebSession to that list, and app204 under v30 and v31. Dropping the one-line change makes both fail with components Unexpected: schemas ; paths./hello.get.parameters[]: Expected 1 values but got 2. mvn test -pl springdoc-openapi-starter-webflux-api is 138 tests, 0 failures.