Update tests that use Spring Boot

[cherylking]

Update tests that reference 2.x Spring Boot to the latest available 2.6.7 release.

Modify tests that reference 1.x Spring Boot to use 2.6.7 instead unless they are duplicates of the 2.x tests.

Also update the Liberty version used as it is quite old at 18.0.0.2.

Tests are located here: https://github.com/OpenLiberty/ci.gradle/tree/main/src/test/resources/sample.springboot

[cherylking]

And here:

https://github.com/OpenLiberty/ci.gradle/blob/main/src/test/groovy/io/openliberty/tools/gradle/TestSpringBootApplication15.groovy

https://github.com/OpenLiberty/ci.gradle/blob/main/src/test/groovy/io/openliberty/tools/gradle/TestSpringBootApplication20.groovy

[cherylking]

According to Anjum, changes are needed in Open Liberty in order to use the latest Spring Boot version. I will create a PR to update the tests to version 2.6.7 and temporarily disable them. Once the next version of OL gets released, I will create another PR to enable the tests for that version of OL.