Akka: re-enable CoordinatedShutdownSpec

[SethTisue]

JDK 11 https://scala-ci.typesafe.com/job/scala-2.13.x-jdk11-integrate-community-build/3464/ queued

JDK 17 https://scala-ci.typesafe.com/job/scala-2.13.x-jdk17-integrate-community-build/414/ queued

[SethTisue]

I thought maybe Akka would be green on JDK 17 these days, but it still isn't:

[akka] Processing subproject: akka-protobuf-v3
[akka] All Dependencies for subproject akka-protobuf-v3:
[akka]    org.scala-lang:scala-compiler:2.13.9-bin-c4b5696:scala-tool->default,optional(default)
[akka]    org.scala-lang:scala-library:2.13.9-bin-c4b5696:scala-tool->default,optional(default)
[akka]    com.lightbend:cloc-plugin:0.0.1-dbuildxa233e22bde20b3fc74c0272e238064a6783b3d4e:plugin->default(compile)
[akka]    com.google.protobuf:protobuf-java:3.16.1:optional;provided
[akka] Running build: akka-protobuf-v3
[akka] [info] Wrote /home/jenkins/workspace/scala-2.13.x-jdk17-integrate-community-build/target-0.9.17/project-builds/akka-2f297226f2cefd2c984fb2299c91d3f19a98527b/akka-protobuf-v3/target/scala-2.13/akka-protobuf-v3-2.6.18-dbuildx2f297226f2cefd2c984fb2299c91d3f19a98527b.pom
[akka] [info] Strategy 'discard' was applied to 2 files (Run the task at debug level to see details)
[akka] [info] Validating all packages are set private or exported for OSGi explicitly...
[akka] [error] java.util.ConcurrentModificationException
[akka] [error] 	at java.base/java.util.TreeMap.callMappingFunctionWithCheck(TreeMap.java:750)
[akka] [error] 	at java.base/java.util.TreeMap.computeIfAbsent(TreeMap.java:604)
[akka] [error] 	at aQute.bnd.osgi.Jar.putResource(Jar.java:259)

this is a longstanding issue: akka/akka#28304

@patriknw I'm noticing some JDK 17 work happening in akka/akka; is it planned to have Akka build on JDK 17, or is the work only about making it run on JDK 17?