Fix flakiness in Log4j2MetricsTest.asyncLogShouldNotBeDuplicated()

[izeye]

Log4j2MetricsTest.asyncLogShouldNotBeDuplicated() failed as follows:

io.micrometer.core.instrument.binder.logging.Log4j2MetricsTest > asyncLogShouldNotBeDuplicated() FAILED
    org.opentest4j.AssertionFailedError: 
    Expecting:
     <0.0>
    to be equal to:
     <1.0>
    but was not.
        at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
        at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
        at java.base/jdk.internal.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
        at io.micrometer.core.instrument.binder.logging.Log4j2MetricsTest.asyncLogShouldNotBeDuplicated(Log4j2MetricsTest.java:174)

This PR fixes the flakiness by waiting for up to 1 second for the meter to be updated.