Bump micrometer-core from 1.8.3 to 1.8.4 (#2528)

Author: dependabot[bot]

apm-agent-plugins/apm-micrometer-plugin/pom.xml

@@ -22,7 +22,7 @@
         <dependency>
             <groupId>io.micrometer</groupId>
             <artifactId>micrometer-core</artifactId>
-            <version>1.8.3</version>
+            <version>1.8.4</version>
             <scope>provided</scope>
         </dependency>
         <dependency>