Bump structs from 1.17 to 1.20

Bumps [structs](https://github.com/jenkinsci/structs-plugin) from 1.17 to 1.20.
- [Release notes](https://github.com/jenkinsci/structs-plugin/releases)
- [Changelog](https://github.com/jenkinsci/structs-plugin/blob/master/CHANGELOG.md)
- [Commits](jenkinsci/structs-plugin@structs-parent-1.17...structs-parent-1.20)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Author: dependabot-preview[bot]

pom.xml

@@ -104,7 +104,7 @@
     <dependency>
       <groupId>org.jenkins-ci.plugins</groupId>
       <artifactId>structs</artifactId>
-      <version>1.17</version>
+      <version>1.20</version>
     </dependency>
     <dependency>
       <groupId>org.jenkins-ci.plugins.workflow</groupId>