Some encryption tests either configured directly to use the plugin, or via include/have_file_key_management_plugin.inc attempt to load the plugin and start the server with encryption options, and then check whether the plugin exists; but the server cannot be started with encryption options if the plugin is not available, so instead of the graceful "skip" we are getting failures on startup.

Maybe the easiest fix is to make all encryption options "loose". There can be other solutions.