chore: upgrade vaadin-testbench to 9.3.8 (#20891)

Co-authored-by: Zhe Sun <[email protected]>

pom.xml

@@ -108,7 +108,7 @@
         <maven.resources.plugin.version>3.0.2</maven.resources.plugin.version>
         <maven.clean.plugin.version>3.4.0</maven.clean.plugin.version>
         <maven.exec.plugin.version>1.6.0</maven.exec.plugin.version>
-        <testbench.version>9.3.7</testbench.version>
+        <testbench.version>9.3.8</testbench.version>
         <jetty.version>12.0.16</jetty.version>
         <properties-maven-plugin.version>1.2.1</properties-maven-plugin.version>
         <build-helper-maven-plugin.version>3.6.0</build-helper-maven-plugin.version>