Update gitlab-org/build/omnibus-mirror/postgres_exporter from 0.14.0 to 0.15.0

The following dependencies have been updated by deps:

• gitlab-org/build/omnibus-mirror/postgres_exporter from 0.14.0 to 0.15.0

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Changelog:

0.15.0 / 2023-10-27
[ENHANCEMENT] Add 1kB and 2kB units #915
[BUGFIX] Add error log when probe collector creation fails #918
[BUGFIX] Fix test build failures on 32-bit arch #919
[BUGFIX] Adjust collector to use separate connection per scrape #936