build(deps): bump org.postgresql:postgresql from 42.5.3 to 42.7.3

Bumps [org.postgresql:postgresql](https://github.com/pgjdbc/pgjdbc) from 42.5.3 to 42.7.3.
- [Release notes](https://github.com/pgjdbc/pgjdbc/releases)
- [Changelog](https://github.com/pgjdbc/pgjdbc/blob/master/CHANGELOG.md)
- [Commits](pgjdbc/pgjdbc@REL42.5.3...REL42.7.3)

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

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

server/build.gradle.kts

@@ -60,7 +60,7 @@ dependencies {
     implementation("org.jetbrains.exposed:exposed-dao:$exposed_version")
     implementation("org.jetbrains.exposed:exposed-jdbc:$exposed_version")
     implementation("org.jetbrains.exposed:exposed-java-time:$exposed_version")
-    implementation("org.postgresql:postgresql:42.5.3")
+    implementation("org.postgresql:postgresql:42.7.3")
     implementation("org.kohsuke:github-api:1.319")
 
     implementation("org.bouncycastle:bcprov-jdk15on:1.70")