fix(deps): bump com.guardsquare:proguard-core from 9.1.4 to 9.1.6

Bumps [com.guardsquare:proguard-core](https://github.com/Guardsquare/proguard-core) from 9.1.4 to 9.1.6.
- [Release notes](https://github.com/Guardsquare/proguard-core/releases)
- [Commits](Guardsquare/proguard-core@v9.1.4...v9.1.6)

---
updated-dependencies:
- dependency-name: com.guardsquare:proguard-core
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <[email protected]>

pom.xml

@@ -50,7 +50,7 @@
       <!-- https://central.sonatype.com/artifact/info.picocli/picocli -->
       <picocli.version>4.7.6</picocli.version>
       <!-- https://central.sonatype.com/artifact/com.guardsquare/proguard-core -->
-      <proguard.version>9.1.4</proguard.version>
+      <proguard.version>9.1.6</proguard.version>
 
       <skip.japicmp.cmp>true</skip.japicmp.cmp>
    </properties>