Fix Nim warning #5580

Job	Run time
Build Android (on Linux)	6m 4s
Build Benchmarks (on Linux) (g++-10)	4m 4s
Build .NET Windows	1m 38s
Build Dart	2m 11s
Check Generated Code (g++-10)	1m 44s
Build .NET Windows (-p:UnsafeByteBuffer=true)	1m 35s
Check Generated Code on Windows	5m 18s
Check Generated Code (clang++-12)	2m 5s
Build Go	2m 49s
Build Java	22s
Build Kotlin Linux	4m 15s
Build Kotlin MacOS	5m 12s
Build Linux (g++-10)	3m 1s
Build Linux C++ (11, g++-10)	2m 42s
Build Linux with -DFLATBUFFERS_NO_FILE_TESTS	2m 47s
Build Linux with out-of-source build location	1m 27s
Build Linux C++ (11, clang++-12)	3m 56s
Build Linux C++ (14, g++-10)	2m 39s
Build Mac (for Intel)	2m 39s
Build Linux (clang++-12)	3m 58s
Build Mac (universal build)	3m 49s
Build Linux C++ (14, clang++-12)	3m 17s
Build Linux C++ (17, g++-10)	4m 30s
Build Nim	2m 7s
Build Python	1m 38s
Build PHP	1m 45s
Build Rust Linux	3m 18s
Build Linux C++ (17, clang++-12)	4m 35s
Build Rust Windows	3m 7s
Build Swift	2m 15s
Build Linux C++ (20, g++-10)	3m 55s
Build Linux C++ (20, clang++-12)	3m 40s
Build Swift Wasm	1m 46s
Build Linux C++ (23, clang++-12)	5m 5s
Build TS	2m 20s
Build Windows 2019	7m 22s
Build Windows 2015	5m 4s
Build Windows 2017	6m 24s
Build Windows C++ (11)	5m 42s
Build Windows C++ (14)	6m 38s
Build Windows C++ (17)	5m 24s
Build Windows C++ (20)	10m 15s
Build Windows C++ (23)	8m 45s
release-digests	0s
provenance	0s
	2h 43m 7s

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