deps: update dependency org.openjdk.jmh:jmh-core to v1.26 (#506)

Author: renovate-bot

google-cloud-spanner/pom.xml

@@ -299,7 +299,7 @@
     <dependency>
       <groupId>org.openjdk.jmh</groupId>
       <artifactId>jmh-core</artifactId>
-      <version>1.25.2</version>
+      <version>1.26</version>
       <scope>test</scope>
     </dependency>
     <dependency>