Use ninja -k option in CI

Some users of the OAI CI complain that since we build with -Werror, it
is difficult to see all warnings/errors and fix them, necessitating
multiple attempts at times to see all warnings. To allow them to see
more warnings, use ninja option -k10 to keep going after errors, and
show more errors at once.

docker/Dockerfile.build.rhel9

@@ -44,6 +44,7 @@ RUN /bin/sh oaienv && \
       --build-e2 --cmake-opt -DXAPP_MULTILANGUAGE=OFF --cmake-opt \
       -DKPM_VERSION=$KPM_VERSION --cmake-opt -DE2AP_VERSION=$E2AP_VERSION \
       --build-lib 'telnetsrv enbscope uescope nrscope' \
+      --build-tool-opt -k10 \
       -w USRP -t Ethernet \
       --noavx512" && \
     echo "---- ldd on executables ----" && \