MINOR: Bump logback.version from 1.5.18 to 1.5.20

Bumps `logback.version` from 1.5.18 to 1.5.20.

Updates `ch.qos.logback:logback-classic` from 1.5.18 to 1.5.20
- [Release notes](https://github.com/qos-ch/logback/releases)
- [Commits](qos-ch/logback@v_1.5.18...v_1.5.20)

Updates `ch.qos.logback:logback-core` from 1.5.18 to 1.5.20
- [Release notes](https://github.com/qos-ch/logback/releases)
- [Commits](qos-ch/logback@v_1.5.18...v_1.5.20)

---
updated-dependencies:
- dependency-name: ch.qos.logback:logback-classic
  dependency-version: 1.5.20
  dependency-type: direct:production
  update-type: version-update:semver-patch
- dependency-name: ch.qos.logback:logback-core
  dependency-version: 1.5.20
  dependency-type: direct:development
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]

pom.xml

@@ -111,7 +111,7 @@ under the License.
     <checkstyle.failOnViolation>true</checkstyle.failOnViolation>
     <error_prone_core.version>2.37.0</error_prone_core.version>
     <checker.framework.version>3.49.3</checker.framework.version>
-    <logback.version>1.5.18</logback.version>
+    <logback.version>1.5.21</logback.version>
     <doclint>none</doclint>
     <additionalparam>-Xdoclint:none</additionalparam>
     <!-- List of add-opens arg line arguments for tests -->