`make test-all RUBYOPT=-w` in the ruby/ruby repo printed the warning.
This change prevents the warning by specifying the content-type
explicitly.

A follow-up to https://github.com/rubygems/rubygems/commit/b70c1bb1503d

https://github.com/rubygems/rubygems/commit/d573af07f6

Signed-off-by: Samuel Giddins <segiddins@segiddins.me>

https://github.com/rubygems/rubygems/commit/a5412d9a0e

If a command requires two MFA authenticated requests, and webauthn is
enabled, then first one will succeed but the second one will fail
because it tries to reuse the OTP code from the first request and that
does not work.

This happens when you have not yet logged in to rubygems.org, or when
you have an API key with invalid scopes for the current operation. In
that case, we need:

* An API request to get a token or change scopes for the one that you
  have.
* Another API request to perform the actual operation.

Instead of trying to reuse the token, make sure it's cleared so we are
asked to authenticate again. We only do this when webauthn is enabled
because reusing TOPT tokens otherwise is allowed and I don't want to
break that.

https://github.com/rubygems/rubygems/commit/669e343935

https://github.com/rubygems/rubygems/commit/99d91c9ed2

https://github.com/rubygems/rubygems/commit/97dbe4cabd

https://github.com/rubygems/rubygems/commit/2d763cfd47

Co-authored-by: Jacques Chester <jacques.chester@shopify.com>

To avoid collisions especially in ruby/ruby

https://github.com/rubygems/rubygems/commit/e6b2359975

https://github.com/rubygems/rubygems/commit/52ae4452c2