[ntuple] fix RNTuple::Merge not passing mergeOpts to RNTupleMerger #12948

Job	Run time
mac13 ARM64 LLVM_ENABLE_ASSERTIONS=On, builtin_zlib=ON	31m 0s
fedora39 LLVM_ENABLE_ASSERTIONS=On, CMAKE_CXX_STANDARD=20	1h 5m 2s
Upload Event Payload	3s
mac14 X64 LLVM_ENABLE_ASSERTIONS=On, CMAKE_CXX_STANDARD=20	1h 7m 41s
Windows 10 x64 Release	1h 9m 33s
alma8 LLVM_ENABLE_ASSERTIONS=On	1h 22m 45s
mac15 ARM64 LLVM_ENABLE_ASSERTIONS=On, CMAKE_CXX_STANDARD=20	34m 1s
Windows 10 x86 Release	1h 49m 31s
alma9 LLVM_ENABLE_ASSERTIONS=On, CMAKE_BUILD_TYPE=Debug	1h 22m 35s
mac-beta ARM64 LLVM_ENABLE_ASSERTIONS=On, CMAKE_CXX_STANDARD=20	37m 9s
ubuntu20 LLVM_ENABLE_ASSERTIONS=On	1h 29m 13s
ubuntu22 imt=Off, LLVM_ENABLE_ASSERTIONS=On, CMAKE_BUILD_TYPE=Debug	1h 23m 40s
ubuntu2404 LLVM_ENABLE_ASSERTIONS=On, CMAKE_BUILD_TYPE=Debug	1h 32m 47s
debian125 LLVM_ENABLE_ASSERTIONS=On, CMAKE_CXX_STANDARD=20	1h 22m 48s
alma9 modules_off runtime_cxxmodules=Off	48m 45s
alma9 march_native CMAKE_BUILD_TYPE=RelWithDebInfo, CMAKE_CXX_FLAGS=-march=native, CMAKE_C_FLAGS=-march=native, fortran=OFF	1h 17m 34s
alma9 arm64 CMAKE_BUILD_TYPE=RelWithDebInfo, ccache=ON	48m 23s
alma9-clang clang LLVM_ENABLE_ASSERTIONS=On, CMAKE_C_COMPILER=clang, CMAKE_CXX_COMPILER=clang++	1h 8m 14s
ubuntu2404-cuda gpu	18m 27s
	19h 49m 11s

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