Bump transitive jnr-posix to 3.1.8

[peel]

Minimum Java 8 seems to be the only major change between series/3.0.x
and series/3.1.x.
Addresses CWE-416[1] w/o known exploit.

1 - https://cwe.mitre.org/data/definitions/416

[peel]

Sample StatsD output using the version including the above datadog4s transitive dependency override:

statsd-1   | [StatsD] 2024-04-02T11:50:13.000Z - {"counters":{"statsd.packets_received":299,"statsd.metrics_received":2887,"datadog.dogstatsd.client.metrics;client=java;client_version=4.2.0;client_transport=udp":20,"datadog.dogstatsd.client.bytes_sent;client=java;client_version=4.2.0;client_transport=udp":315961,"datadog.dogstatsd.client.packets_sent;client=java;client_version=4.2.0;client_transport=udp":297,"datadog.dogstatsd.client.aggregated_context;client=java;client_version=4.2.0;client_transport=udp":6,"datadog.dogstatsd.client.metrics_by_type;client=java;client_version=4.2.0;client_transport=udp;metrics_type=gauge":8,"datadog.dogstatsd.client.metrics_by_type;client=java;client_version=4.2.0;client_transport=udp;metrics_type=count":4,"datadog.dogstatsd.client.metrics_by_type;client=java;client_version=4.2.0;client_transport=udp;metrics_type=distribution":8,"datadog.dogstatsd.client.aggregated_context_by_type;client=java;client_version=4.2.0;client_transport=udp;metrics_type=gauge":5,"datadog.dogstatsd.client.aggregated_context_by_type;client=java;client_version=4.2.0;client_transport=udp;metrics_type=count":1,"snowplow.collector.headers_time;method=GET":128,"snowplow.collector.requests_latency;status_code=200;status_bucket=2xx;method=GET":166,"snowplow.collector.requests_count;status_code=200;status_bucket=2xx;method=GET":4}}
statsd-1   | [StatsD] 2024-04-02T12:08:52.000Z - {"counters":{"statsd.packets_received":217,"statsd.metrics_received":1904,"datadog.dogstatsd.client.bytes_sent;client=java;client_version=4.2.0;client_transport=udp":210081,"datadog.dogstatsd.client.packets_sent;client=java;client_version=4.2.0;client_transport=udp":217}}