Incompatibility between zend-diactoros and psr-http-message-bridge versions: require symfony/psr-http-message-bridge >=1.1.2

I ran into a compatibility issue between Zend Diactoros and Symfony psr-http-message-bridge as pointed out in #3045306-6: Paypal payment fails with InvalidArgumentException in MessageTrait .

Either Diactoros should stay at 1.8.5 or Symfony psr-http-message-bridge should be upgraded to 1.2.0. However psr-http-message-bridge 1.2.0 requires PHP 7.1, hence it was not installed on my php 7.0 Debian 9 (stable) box.

So I would see three solutions:

• Pin Diactoros to 1.8.5.
• Create an alternative version of psr-http-message-bridge (eg. 1.1.2) which would fix the issue but not require php 7.1.
• Or a very harsh measure: have Drupal require php 7.1. (it is EOL, but still part of eg. Debian Stable)

What is the preferred Drupal way in this? I'd be happy to relay this issue to the psr-http-message-bridge repo.