CI: Fix OCI-full builds

[amotl]

After mysqlclient 2.2.0 ^1 has been released, the build needs the pkg-config package. Otherwise, the build fails ^2.

Exception: Can not find valid pkg-config name.
Specify MYSQLCLIENT_CFLAGS and MYSQLCLIENT_LDFLAGS env vars manually

[codecov[bot]]

Codecov Report

Patch and project coverage have no change.

Comparison is base (288392f) 47.94% compared to head (546f5b6) 47.94%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #678 +/- ## ======================================= Coverage 47.94% 47.94% ======================================= Files 81 81 Lines 3917 3917 ======================================= Hits 1878 1878 Misses 2039 2039 ``` | Flag | Coverage Δ | | |---|---|---| | unittests | `47.94% <ø> (ø)` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=mqtt-tools#carryforward-flags-in-the-pull-request-comment) to find out more.

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