Quartz 2.3.0 and other RC versions were released with a wrong c3p0 groupId. Issue should be fixed in subsequent versions, but adding dependency as stated in https://stackoverflow.com/a/50860439/2144470 it's also a solution.

So it should work changing dependency to:

    <dependency>
        <groupId>org.quartz-scheduler</groupId>
        <artifactId>quartz</artifactId>
        <version>2.3.2</version>
    </dependency>