deps: update dependency ch.qos.logback:logback-core to v1.3.15 [security]

Author: renovate-bot

java-showcase/gapic-showcase/pom.xml

@@ -18,7 +18,7 @@
 
   <properties>
     <gapic-showcase.version>0.36.2</gapic-showcase.version>
-    <slf4j1-logback.version>1.2.13</slf4j1-logback.version>
+    <slf4j1-logback.version>1.3.15</slf4j1-logback.version>
   </properties>
 
   <build>