Unit tests fail with php 5.4 to 7.1 in Ubuntu Focal and later

[gggeek]

All the tests using the "ssl stream wrapper" transport currently fail when run on Ubuntu 20/22 with php 5.4, 5.5, 5.6, 7.0 and 7.1.

The same tests pass both when using different php versions, and when using different ubuntu versions.

This makes me think that there is an issue in the usage of the underlying ssl library by php - it might be due to how the Sury .deb packages are compiled, or that we are just missing some stream context options...