If the standard_format test occurs exactly at a second boundary (i.e. no milliseconds towards the next second), it will fail, since the expected string format for the date will contain no fractional 0s. This means this test will fail ~1 in ever thousand runs.

We should make the test more robust to such failures by ensuring the fractional zeroes are always included in the expected format, or by picking a static date to use for all test runs.

example failure: https://evergreen.mongodb.com/task/rust_bson_tests_test_0608c84af9cbbf71e93e6a38e516936f9a0bf6c4_21_09_02_16_12_04/0