Update tests for STATSD_DEBUG=True

[jwhitlock]

When DJANGO_STATSD_ENABLED=True and STATSD_DEBUG=True, log messages like these are emitted:

{"Timestamp": 1717537908384410880, "Type": "markus", "Logger": "fx-private-relay", "Hostname": "jwhitlock-MB-M2.lan", "EnvVersion": "2.0", "Severity": 6, "Pid": 66599, "Fields": {"rid": null, "msg": "METRICS|2024-06-04 21:51:48|timing|fx.private.relay.response|55.711984634399414|#status:200,view:<static_file>,method:GET"}}
{"Timestamp": 1717537908517943040, "Type": "markus", "Logger": "fx-private-relay", "Hostname": "jwhitlock-MB-M2.lan", "EnvVersion": "2.0", "Severity": 6, "Pid": 66599, "Fields": {"rid": null, "msg": "METRICS|2024-06-04 21:51:48|timing|fx.private.relay.response|82.79109001159668|#status:200,view:<static_file>,method:GET"}}

The second message has details about the response timing metric:

METRICS|2024-06-04 21:51:48|timing|fx.private.relay.response|82.79109001159668|#status:200,view:<static_file>,method:GET

This can be useful for local debugging or understanding metrics. It can also be very noisy, and break tests that do not expect them. This PR updates the some tests to filter out the metrics logs.

[jwhitlock]

No production code, so self-reviewing.