Update to lastest version of bcprov-jdk18on so Dependabot will stop complaining.

Note that this is only used in a 'test' scope anyway and to the best of
my knowlege, none of the test uses of any of the vulnerable Bouncy Castle methods.

Author: kwwall

pom.xml

@@ -303,8 +303,8 @@
         </dependency>
         <dependency>
             <groupId>org.bouncycastle</groupId>
-            <artifactId>bcprov-jdk15on</artifactId>
-            <version>1.70</version>
+            <artifactId>bcprov-jdk18on</artifactId>
+            <version>1.78.1</version>
             <scope>test</scope>
         </dependency>
         <dependency>