[jdk11u-dev] RFR: 8272197: Update 11u GHA workflow with Shenandoah configurations

[Aleksey Shipilev]

I have noticed that 11u GHA workflow builds/tests without Shenandoah. This is because Shenandoah is not enabled by default in 11u, in contrast to mainline. Which means the workflow that we have picked from mainline does not enable Shenandoah.

Instead of changing the build defaults for 11u, I suggest we add Shenandoah configs to testing.

Example run:
https://github.com/shipilev/jdk11u-dev/runs/3288861982

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Commit messages:
 - 8272197: Update 11u GHA workflow with Shenandoah configurations

Changes: https://git.openjdk.java.net/jdk11u-dev/pull/216/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk11u-dev&pr=216&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8272197
  Stats: 10 lines in 1 file changed: 10 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk11u-dev/pull/216.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk11u-dev pull/216/head:pull/216

PR: https://git.openjdk.java.net/jdk11u-dev/pull/216