build-unit-test-docker: Update to gcc-14

Align with the recent Yocto update in OpenBMC[1], which pulls in gcc-14.

[1]: https://github.com/openbmc/openbmc/commit/edff49234e31f23dc79f823473c9e286a21596c1

Change-Id: If65df474997198d7e3d0aa686838b302a9ce87ef
Signed-off-by: Andrew Jeffery <andrew@codeconstruct.com.au>
1 file changed