Fix ninja build failing due to missing protobuf reference

It seems that since !942 (merged), building with Ninja will fail with this error (running ./build_deploy.sh -r):

[14/1011] Building CXX object eos_cta/CMakeFiles/ctagrpc.dir/cta_admin.grpc.pb.cc.o
FAILED: eos_cta/CMakeFiles/ctagrpc.dir/cta_admin.grpc.pb.cc.o 
ccache /usr/bin/c++  -I/shared/CTA/build_rpm/RPM/BUILD/cta-5-fafb6f06fa -I/shared/CTA/build_rpm/RPM/BUILD/cta-5-fafb6f06fa/build -fPIC -pedantic -Wall -Wextra -Werror -Wno-unused-parameter -fstack-protector-all -std=c++17 -g -fPIC -MD -MT eos_cta/CMakeFiles/ctagrpc.dir/cta_admin.grpc.pb.cc.o -MF eos_cta/CMakeFiles/ctagrpc.dir/cta_admin.grpc.pb.cc.o.d -o eos_cta/CMakeFiles/ctagrpc.dir/cta_admin.grpc.pb.cc.o -c /shared/CTA/build_rpm/RPM/BUILD/cta-5-fafb6f06fa/build/eos_cta/cta_admin.grpc.pb.cc
/shared/CTA/build_rpm/RPM/BUILD/cta-5-fafb6f06fa/build/eos_cta/cta_admin.grpc.pb.cc:5:10: fatal error: cta_admin.pb.h: No such file or directory
    5 | #include "cta_admin.pb.h"
      |          ^~~~~~~~~~~~~~~~
compilation terminated.
[27/1011] Building CXX object eos_grpc_client/CMakeFiles/EosGrpcClient.dir/GrpcClient.cpp.o
ninja: build stopped: subcommand failed.
error: Bad exit status from /var/tmp/rpm-tmp.HX7WYE (%build)

I only noticed this after the linked MR was merged in main.