Bump r2dbc-postgresql in /modules/postgresql

Bumps [r2dbc-postgresql](https://github.com/r2dbc/r2dbc-postgresql) from 0.8.12.RELEASE to 0.8.13.RELEASE.
- [Release notes](https://github.com/r2dbc/r2dbc-postgresql/releases)
- [Changelog](https://github.com/pgjdbc/r2dbc-postgresql/blob/v0.8.13.RELEASE/CHANGELOG)
- [Commits](pgjdbc/r2dbc-postgresql@v0.8.12.RELEASE...v0.8.13.RELEASE)

---
updated-dependencies:
- dependency-name: io.r2dbc:r2dbc-postgresql
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]

modules/postgresql/build.gradle

@@ -7,14 +7,14 @@ dependencies {
     api project(':jdbc')
 
     compileOnly project(':r2dbc')
-    compileOnly 'io.r2dbc:r2dbc-postgresql:0.8.12.RELEASE'
+    compileOnly 'io.r2dbc:r2dbc-postgresql:0.8.13.RELEASE'
 
     testImplementation project(':jdbc-test')
     testImplementation project(':test-support')
     testImplementation 'org.postgresql:postgresql:42.4.2'
 
     testImplementation testFixtures(project(':r2dbc'))
-    testImplementation 'io.r2dbc:r2dbc-postgresql:0.8.11.RELEASE'
+    testImplementation 'io.r2dbc:r2dbc-postgresql:0.8.13.RELEASE'
 
     compileOnly 'org.jetbrains:annotations:23.0.0'
 }