Update SnakeYAML-Engine to 3.0.1

[headius]

There are two CVEs in Guava, which is a test-scoped dependency of this library. Guava is not shipped with the library so these CVEs do not affect users, but the dependency may trigger security tools. We update to avoid this false positive.

https://www.cve.org/CVERecord?id=CVE-2023-2976

https://www.cve.org/CVERecord?id=CVE-2020-8908

Fixes #780

[chadlwilson]

snakeyaml-engine 3.x requires Java 11. Was it intentional to drop support for Java 8?

https://bitbucket.org/snakeyaml/snakeyaml-engine/wiki/Changes

The tests here don't run across java versions sufficiently to validate these types of things; they just use either the actions runner default JDK or the latest default on the given Ubuntu version.

[chadlwilson]

If this was unintentional, and you're open to it, im happy to either submit a PR to

1. run tests under java 8 and a min supported JRuby version (not solely jruby-head)
2. OR to use deterministic supported java versions for each JRuby version under test
3. OR to just use a standard maven plugin to check the jar dependencies are java 8 compatible via the existing Mavenfile

#1 may be more maintainable & understandable for non Java experts in the team (and also validate the code under 8 via tests), but does add more to the build.

For @hsbt benefit, JRuby 9.3 (EOL but still supported by this gem via its constraints) and 9.4 (nearing EOL) both support Java 8. JRuby 10.0+ supports Java 21 minimum.