Update CI to use Matrix Build to test against different Guava versions

[cowtowncoder]

Similar to Joda module's GH Action:

https://github.com/FasterXML/jackson-datatype-joda/blob/2.18/.github/workflows/main.yml

it'd make sense to set up Matrix build to try out couple of different Guava versions:

1. The minimum version we can/want to support (less than default dep version, usually)
2. Current default dependency version
3. Latest available (assuming that works)

This should help avoid breakages wrt different Guava versions since we currently support a wide range.

Note: we probably want to reduce set of combinations (JDK + Guava) somehow from full cartesian product to avoid excessive processing (I don't think we are close to quota but just in case).

[cowtowncoder]

Guava versions to test:

• Minimum (since 2.16): 20.0
• Default (for now): 25.1-jre
• Maximum (latest): 33.1.0-jre

[cowtowncoder]

Done, should be cleaner, works as expected.