Multiple errors at once, crashes, minus values where no should be.

[scolastico]

Describe the bug

Error messages, crashes, [see below for more]...

To Reproduce

Steps to reproduce the behavior:

1. Default usage procedere

Expected behavior

No error messages and no 'needs more runners' with a value below one.

Additional context

Configuration 'scolastico-dev:latest' needs 2 more runner(s)...
Starting runner '44FA242FB65417AB540413AC8FC49A20'...
Starting runner '07E8A170B3C66DA307E3B9C41D779D01'...
Configuration 'scolastico-dev:debian-buster' needs 1 more runner(s)...
Starting runner 'CAA06B455E02A4B3A1C92DB2FF30055A'...
Configuration 'annoy-others:latest' needs 2 more runner(s)...
Starting runner 'AEDFD66F80052D1397BEBCFA50C8FE9E'...
Starting runner '4735C476C37CF54BAEE4089D91064921'...
Message: null
StackTrace:
java.util.ConcurrentModificationException
        at java.base/java.util.HashMap$HashIterator.nextNode(HashMap.java:1584)
        at java.base/java.util.HashMap$KeyIterator.next(HashMap.java:1607)
        at me.scolastico.runner.manager.routines.scheduler.CheckRunnersRoutine.execute(CheckRunnersRoutine.java:49)
        at me.scolastico.tools.routine.RoutineManager.execute(RoutineManager.java:49)
        at me.scolastico.tools.routine.RoutineManager.startNotAsynchronously(RoutineManager.java:96)
        at me.scolastico.runner.manager.routines.starting.SchedulerRoutine$1.run(SchedulerRoutine.java:43)
        at java.base/java.lang.Thread.run(Thread.java:831)

Configuration 'scolastico-dev:latest' needs -2 more runner(s)...
Configuration 'scolastico-dev:debian-buster' needs -1 more runner(s)...
Configuration 'annoy-others:latest' needs -2 more runner(s)...
Configuration 'annoy-others:debian-buster' needs 1 more runner(s)...
Starting runner 'BF0AD30746A282C2D5C726F1B734EEF8'...
Configuration 'scolastico-dev:latest' needs -2 more runner(s)...
Configuration 'annoy-others:latest' needs -2 more runner(s)...