Only generate valid names for `FsPath` tests #279

Job	Run time
stylish-haskell (9.6.4, 3.10.3.0, ubuntu-latest)	2m 52s
cabal-check (9.6.4, 3.10.3.0, ubuntu-latest)	2m 13s
cabal-fmt (9.6.4, 3.10.3.0, ubuntu-latest)	2m 26s
build (8.10.7, 3.10.3.0, ubuntu-latest)	1m 57s
build (8.10.7, 3.10.3.0, windows-latest)	4m 25s
build (8.10.7, 3.10.3.0, macOS-13)	3m 51s
build (9.2.8, 3.10.3.0, ubuntu-latest)	1m 54s
build (9.2.8, 3.10.3.0, windows-latest)	4m 48s
build (9.2.8, 3.10.3.0, macOS-13)	2m 39s
build (9.4.8, 3.10.3.0, ubuntu-latest)	2m 36s
build (9.4.8, 3.10.3.0, windows-latest)	4m 40s
build (9.4.8, 3.10.3.0, macOS-13)	8m 45s
build (9.6.4, 3.10.3.0, ubuntu-latest)	2m 44s
build (9.6.4, 3.10.3.0, windows-latest)	4m 46s
build (9.6.4, 3.10.3.0, macOS-13)	5m 43s
build (9.8.2, 3.10.3.0, ubuntu-latest)	1m 10s
build (9.8.2, 3.10.3.0, windows-latest)	1m 59s
build (9.8.2, 3.10.3.0, macOS-13)	7m 0s
	1h 6m 28s

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