Update threading for action PerlToggleSourceRootAction

[hurricup]

com.intellij.diagnostic.PluginException: `ActionUpdateThread.OLD_EDT` is deprecated and going to be removed soon. 'com.perl5.lang.perl.idea.configuration.settings.sdk.PerlToggleSourceRootAction' must override `getActionUpdateThread` and chose EDT or BGT. See ActionUpdateThread javadoc. [Plugin: com.perl5]
	at com.intellij.diagnostic.PluginProblemReporterImpl.createPluginExceptionByClass(PluginProblemReporterImpl.java:23)
	at com.intellij.diagnostic.PluginException.createByClass(PluginException.java:90)
	at com.intellij.diagnostic.PluginException.reportDeprecatedUsage(PluginException.java:125)
	at com.intellij.openapi.actionSystem.ActionUpdateThreadAware.getActionUpdateThread(ActionUpdateThreadAware.java:21)
	at com.intellij.openapi.actionSystem.AnAction.getActionUpdateThread(AnAction.java:199)

https://camelcade.myjetbrains.com/youtrack/issue/CAMELCADE-18908/com.intellij.diagnostic.PluginException-ActionUpdateThread.OLDEDT-is-depreca