build-unit-test-docker: update googletest

Googletest 1.14 has issues with clang-18.  Update to 1.15.2 which
seems to no longer have the issues.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: Ic31cd021ea17ba6d1a9f81399f8deaa86bdb5900
1 file changed