Add gix-commitgraph::File fuzzer #3791

Job	Run time
test-fast (windows-latest)	12m 46s
pure-rust-build	1m 59s
test-fast (macos-latest)	6m 0s
test-32bit (armv7-linux-androideabi)	1m 41s
test-fast (ubuntu-latest)	3m 22s
cargo-deny (advisories)	27s
lint	3m 55s
installation (win-msvc)	7m 21s
cargo-deny (bans licenses sources)	27s
installation (win-gnu)	7m 31s
installation (win32-msvc)	7m 2s
test	19m 24s
installation (win32-gnu)	7m 24s
WebAssembly (wasm32-unknown-unknown)	48s
WebAssembly (wasm32-wasi)	52s
	1h 20m 59s

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