fix: Accept header usage

[dadrus]

Related issue(s)

Not documented. Encountered during the review of #1043

Checklist

• I agree to follow this project's Code of Conduct.
• I have read, and I am following this repository's Contributing Guidelines.
• I have read the Security Policy.
• I have added tests that prove the correctness of my implementation.

Description

In many places, heimdall implements useful defaults. Among other things, these are HTTP headers. On of such defaults is the Accept header, which has unfortunately been set as Accept-Type, which just does not exist. In principle, there should not be any issues because of this, as many implementations are just ignoring such headers, especially in m2m contexts.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (2beb9b0) 89.20% compared to head (8f9e5d5) 89.20%.
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1107   +/-   ##
=======================================
  Coverage   89.20%   89.20%           
=======================================
  Files         246      246           
  Lines       10367    10367           
=======================================
  Hits         9248     9248           
  Misses        881      881           
  Partials      238      238           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.