The GitHub Actions job "Linux Tests (ubuntu-24.04, 8.6, 8.2, replica_set)" reports 7 failures. There are two root causes.

1. run-tests.php runs tests in parallel by default since PHP 8.6

The job log shows "Spawning 4 workers... Done" although TEST_PHP_ARGS does not contain -j. In PHP 8.5 and earlier, the default is a single
process.

The test suite is not parallel safe, because all workers share a single MongoDB deployment:

• fail points
  configured with failCommand apply to the whole server, so a fail point with times: 1 can be consumed by another test
  running at the same time
• several tests use fixed namespaces, for example the CSFLE key vault collection, so documents
  created by one test are visible to another
• skip_if_not_clean() only checks the state before the test starts, it does
  not prevent concurrent writes

This produces failures in tests/clientEncryption, tests/writeResult and
tests/writeConcernError. The set of failing tests changes between runs.

2. is_integer() is deprecated since PHP 8.6

Six tests in tests/apm call is_integer() and now print "Deprecated: Function is_integer() is deprecated since 8.6, use is_int() instead".

Fix

• pass -j1 in TEST_PHP_ARGS for GitHub Actions and Evergreen, with a comment explaining that the suite cannot run in parallel against a shared server
• replace is_integer() with is_int() in the
  affected tests