* Bump libmongoc to 1.19-dev
* PHPC-1890: Constant for ReadConcern snapshot level
* Move Manager::startSession() error test and delete obsolete test
The deleted error test was redundant. It was originally created in ca4c52eb1c to work around changes in PHP 8, but 60febd0f28 subsequently reintroduced a portable version of the test case.
Also adds missing SKIPIF to startSession test.
* PHPC-1889: Session snapshot option
* PHPC-1875: Session with snapshot=true cannot perform writes
* PHPC-1876: Session with snapshot=true requires MongoDB 5.0+