chore(deps): update postgres:18 docker digest to b870e6b (#2035)

This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| postgres | service | digest | `38d5c9d` -> `b870e6b` |

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.github/workflows/test.yml

@@ -111,7 +111,7 @@ jobs:
         ports:
           - 3306:3306
       migration-smoke-db-postgres:
-        image: postgres:18@sha256:38d5c9d522037d8bf0864c9068e4df2f8a60127c6489ab06f98fdeda535560f9
+        image: postgres:18@sha256:b870e6b96354b3ed4b8737382093b22e5db2bf48b2fd97c009d3a85697cd0949
         env:
           POSTGRES_PASSWORD: vikunjatest
           POSTGRES_DB: vikunjatest