build-unit-test-docker: Bump to Boost 1.75

Boost 1.75 is now available in poky, so update it in CI.

This will allow us to use the no-rtti flag in our builds again.

Change-Id: I85c08cf615150cdf1663501068bbccb3df5f2eb0
Signed-off-by: Jason M. Bills <jason.m.bills@linux.intel.com>
1 file changed