[ntupleutil] exporter: check that the output file is writable #15386

Job	Run time
Windows 10 x64 Release	1h 1m 46s
Windows 10 x86 Release	59m 39s
mac13 ARM64 LLVM_ENABLE_ASSERTIONS=On, builtin_zlib=ON	22m 27s
mac14 X64 LLVM_ENABLE_ASSERTIONS=On, CMAKE_CXX_STANDARD=20	56m 13s
mac15 ARM64 LLVM_ENABLE_ASSERTIONS=On, CMAKE_CXX_STANDARD=20	26m 20s
fedora40 LLVM_ENABLE_ASSERTIONS=On, CMAKE_CXX_STANDARD=20	41m 56s
mac-beta ARM64 LLVM_ENABLE_ASSERTIONS=On, CMAKE_CXX_STANDARD=20	36m 53s
fedora41 LLVM_ENABLE_ASSERTIONS=On	35m 49s
alma8 LLVM_ENABLE_ASSERTIONS=On	25m 2s
Upload Event Payload	4s
alma9 LLVM_ENABLE_ASSERTIONS=On, CMAKE_BUILD_TYPE=Debug	57m 31s
ubuntu22 imt=Off, LLVM_ENABLE_ASSERTIONS=On, CMAKE_BUILD_TYPE=Debug	1h 32m 6s
ubuntu2404 LLVM_ENABLE_ASSERTIONS=On, CMAKE_BUILD_TYPE=Debug	1h 59m 38s
ubuntu2410 LLVM_ENABLE_ASSERTIONS=On, CMAKE_BUILD_TYPE=Debug	1h 40m 36s
debian125 LLVM_ENABLE_ASSERTIONS=On, CMAKE_CXX_STANDARD=20	42m 41s
alma9 modules_off runtime_cxxmodules=Off	34m 35s
alma9 march_native CMAKE_BUILD_TYPE=RelWithDebInfo, CMAKE_CXX_FLAGS=-march=native, CMAKE_C_FLAGS=-march=native, fortran=OFF	23m 33s
alma9 arm64 CMAKE_BUILD_TYPE=RelWithDebInfo	36m 49s
alma9-clang clang LLVM_ENABLE_ASSERTIONS=On, CMAKE_C_COMPILER=clang, CMAKE_CXX_COMPILER=clang++	42m 45s
	15h 16m 23s

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