Fixed failing test and added other test branch

[big-kahuna-burger]

Closes #63

Looking into work done in #64 and comments there, I've found out the issue with and without flushing headers.

• added extra test so both cases are tested
• refactored duplicated http calls for error path into a function
• removed support for older runtimes

[big-kahuna-burger]

@Fdawgs @mcollina do you want to let the action run on this one please?

[big-kahuna-burger]

Merging this makes #64 obsolete so you might want to close that.