Fix ReaderApplication request header to Accept

[csarven]

For the requirement #reader-application-webid-profile, when the ReaderApplication is using GET, the intended header is Accept (as opposed to Content-Type).

This PR includes "Corrections that do not add new features" ( https://www.w3.org/2023/Process-20231103/#class-3 ) in particular technically:

makes conforming data, processors, or other conforming agents become non-conforming according to the new version

but since this is more of an error in the spec, it also technically:

makes non-conforming data, processors, or other agents become conforming.

Which is a good thing.

[elf-pavlik]

When an apparent bug is being fixed, I would immediately merge it.