tests: Upgrade logback to 1.5.25 in tests (googleapis#4103)

We received vulnerability report for logback v1.5.21. Even though it is
only used in tests and does not affect customers, it is still good to
upgrade logback to 1.5.25 in tests.

Author: blakeli0

java-showcase-3.21.0/gapic-showcase/pom.xml

@@ -20,7 +20,7 @@
     <gapic-showcase.version>0.36.2</gapic-showcase.version>
     <!-- This is the last version supporting slf4j 1.x, do not upgrade -->
     <slf4j1-logback.version>1.2.13</slf4j1-logback.version>
-    <slf4j2-logback.version>1.5.21</slf4j2-logback.version>
+    <slf4j2-logback.version>1.5.25</slf4j2-logback.version>
   </properties>
 
   <build>

java-showcase-3.25.8/gapic-showcase/pom.xml

@@ -20,7 +20,7 @@
     <gapic-showcase.version>0.36.2</gapic-showcase.version>
     <!-- This is the last version supporting slf4j 1.x, do not upgrade -->
     <slf4j1-logback.version>1.2.13</slf4j1-logback.version>
-    <slf4j2-logback.version>1.5.21</slf4j2-logback.version>
+    <slf4j2-logback.version>1.5.25</slf4j2-logback.version>
   </properties>
 
   <build>

java-showcase/gapic-showcase/pom.xml

@@ -20,7 +20,7 @@
     <gapic-showcase.version>0.36.2</gapic-showcase.version>
     <!-- This is the last version supporting slf4j 1.x, do not upgrade -->
     <slf4j1-logback.version>1.2.13</slf4j1-logback.version>
-    <slf4j2-logback.version>1.5.21</slf4j2-logback.version>
+    <slf4j2-logback.version>1.5.25</slf4j2-logback.version>
   </properties>
 
   <build>