Add support for Gradle 8

[eamansour]

Why?

See galasa-dev/projectmanagement#1652

Changes

• Added a condition around a workaround applied in the SDV manager's build.gradle to allow the checkstyle plugin to work with Gradle 6, which breaks Gradle 7 and 8 builds
• Updated the jacocoMerge task since the JacocoMerge task was deprecated in favour of JacocoReport
  • JacocoReport cannot produce a .exec file, so the published managers code coverage report artifact is now in XML format
• Enabled Jacoco report generation for subprojects applying the galasa.manager plugin

[galasa-team]

Build successful