Bump jetty.version from 12.0.19 to 12.0.20 (#435)

Bumps `jetty.version` from 12.0.19 to 12.0.20.

Updates `org.eclipse.jetty:jetty-bom` from 12.0.19 to 12.0.20
- [Release notes](https://github.com/jetty/jetty.project/releases)
- [Commits](jetty/jetty.project@jetty-12.0.19...jetty-12.0.20)

Updates `org.eclipse.jetty.ee9:jetty-ee9-bom` from 12.0.19 to 12.0.20
- [Release notes](https://github.com/jetty/jetty.project/releases)
- [Commits](jetty/jetty.project@jetty-12.0.19...jetty-12.0.20)

---
updated-dependencies:
- dependency-name: org.eclipse.jetty:jetty-bom
  dependency-version: 12.0.20
  dependency-type: direct:production
  update-type: version-update:semver-patch
- dependency-name: org.eclipse.jetty.ee9:jetty-ee9-bom
  dependency-version: 12.0.20
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

pom.xml

@@ -37,7 +37,7 @@
   <properties>
     <revision>8.8</revision>
     <changelist>-SNAPSHOT</changelist>
-    <jetty.version>12.0.19</jetty.version>
+    <jetty.version>12.0.20</jetty.version>
     <gitHubRepo>jenkinsci/winstone</gitHubRepo>
     <spotless.check.skip>false</spotless.check.skip>
   </properties>