@jtnord and @imod seem to concur that M2ReleaseArgumentInterceptorAction is never used after the build completes.
Therefore there is no purpose in making any of its fields nontransient.
(Ideally the action would not be stored in build.xml at all, using TransientBuildActionFactory,
but MavenModuleSetBuildExecution does not consult Run.getTransientActions so this would not work.)
This simplifies the handling of scmPassword: no Secret storage is required.
That in turn simplifies testing: no JenkinsRule is needed.