build(deps): bump org.postgresql:postgresql in /modules/gs-tree (#699)

Bumps [org.postgresql:postgresql](https://github.com/pgjdbc/pgjdbc) from 42.6.0 to 42.7.0.
- [Release notes](https://github.com/pgjdbc/pgjdbc/releases)
- [Changelog](https://github.com/pgjdbc/pgjdbc/blob/master/CHANGELOG.md)
- [Commits](pgjdbc/pgjdbc@REL42.6.0...REL42.7.0)

---
updated-dependencies:
- dependency-name: org.postgresql:postgresql
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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modules/gs-tree/pom.xml

@@ -96,7 +96,7 @@
  <dependency>
  <groupId>org.postgresql</groupId>
  <artifactId>postgresql</artifactId>
- <version>42.6.0</version>
+ <version>42.7.0</version>
  </dependency>
  <dependency>
  <groupId>org.mapstruct</groupId>