Review the JDK version support matrix for a next release/tests

[DiegoPino]

What?

Current tests include JDK 11, see

cantaloupe/.github/workflows/release.yml

Line 13 in 21057cf

java-version: '11'

JDK11 is End of Life.

With #653 coming in, for a 6.0.0 release we could probably drop old JDK versions and focus only on LTS/still valid versions of Java

see https://endoflife.date/oracle-jdk

[glenrobson]

No objections recieved so far. Cantaloupe dev meeting on 3rd of July raised no objections to dropping JDK11.

[glenrobson]

Which versions do we want to support?

• 17 and 21
• 22 looking to future

Go by the support for OpenJDK: https://access.redhat.com/articles/1299013#OpenJDK_Life_Cycle

(which is much clearer than Oracles page).