Simplify build jobs using a matrix

[saurabhyadav1985]

Motivation:
Reduce duplication in the GitHub Actions workflow unit-tests #83

Modification:
Refactored three jobs into one, now will build using strategy.matrix.version

Result:
Jobs should build for Java 8, 11 and 17 version.

[jchrys]

Thank you very much for your PR! Just one small thing.

• Could you please rebase and squash the changes to create a single commit?

Could you please add a line separator in the commit message, as shown below, to improve readability?

Motivation: 
Reduce ...

Modification: 
Refactored...

Result: 
Jobs...

[saurabhyadav1985]

Hey can you please delete my fork so I can fork again and raise PR as I am unable to squash into one commit

[jchrys]

You don't need to delete your fork to achieve this; you can do it by yourself.

Try the following steps:

$ git checkout {yourbranch}
$ git rebase -i trunk
Squash all commits except the top one.
Create a commit message.
$ git push --force

[jchrys]

I squash merged to make it a single commit.
Thanks a lot!