Use the latest minor version of PostgreSQL 10 in CI tests

What does this MR do?

Changes to use the latest minor version of PostgreSQL 10 in CI tests.

Why

From version 10 of PostgreSQL, the minor versioning is the last part of the version number. 10 is equivalent to 9.6.

https://www.postgresql.org/support/versioning/

Minor releases are numbered by increasing the last part of the version number. Beginning with PostgreSQL 10, this is the second part of the version number, e.g. 10.0 to 10.1; for older versions this is the third part of the version number, e.g. 9.5.3 to 9.5.4.

• 10.9, 10

cf. https://hub.docker.com/_/postgres

Previous upgrade was in !28020 (merged).

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• [n/a] Documentation created/updated or follow-up review issue created
• Code review guidelines
• [n/a] Merge request performance guidelines
• [n/a] Style guides
• [n/a] Database guides
• [n/a] Separation of EE specific content

Performance and testing

• [-] Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• [-] Tested in all supported browsers

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• [n/a] Label as security and @ mention @gitlab-com/gl-security/appsec
• [n/a] The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• [n/a] Security reports checked/validated by a reviewer from the AppSec team