devel/opentelemetry-cpp: fix build error

Added devel/c4core as a lib dependency:

> Running Q/A tests (stage-qa)

Error: /usr/local/lib/libopentelemetry_configuration.so.1.24.0 is linked to /usr/local/lib/libc4core.so.0.2.6 from devel/c4core but it is not declared as a dependency
Warning: you need LIB_DEPENDS+=libc4core.so:devel/c4core
Warning: you might not need LIB_DEPENDS on libcurl.so
Warning: you might not need LIB_DEPENDS on libgtest.so

• Error code 1

Approved by: just-fix-it