Fix typos in GraphQL over HTTP agenda (#388)

Author: martinbonnin

working-group/agendas/2026/04-Apr/23-graphql-over-http-wg-april-2026.md

@@ -120,3 +120,5 @@ We typically meet on the last Thursday of the month.
    - https://github.com/graphql/graphql-over-http/pull/385
 1. Move "unknown parameters" so that it's common to both GET and POST requests
    - https://github.com/graphql/graphql-over-http/pull/384
+1. Fix typos
+   - https://github.com/graphql/graphql-over-http/pull/387