BUG: fix handling of files installed via install_subdir #1983

Job	Run time
pyston (3.8)	2m 43s
cygwin (3.9)	6m 45s
msvc (3.11)	4m 9s
homebrew (3.8)	6m 22s
homebrew (3.11)	4m 10s
test (ubuntu, 3.7)	1m 58s
test (ubuntu, 3.11)	2m 43s
test (macos, 3.7)	3m 5s
test (macos, 3.11)	3m 43s
test (windows, 3.7)	6m 2s
test (windows, 3.11)	6m 15s
test (ubuntu, pypy-3.9)	5m 26s
test (ubuntu, 3.8)	2m 22s
test (ubuntu, 3.9)	2m 26s
test (ubuntu, 3.10)	2m 17s
test (ubuntu, 3.12-dev)	3m 56s
test (ubuntu, 3.11, ~=0.63.3)	2m 48s
test (ubuntu, 3.11, ~=0.64.0)	2m 54s
test (ubuntu, 3.11, ~=1.0.0)	2m 21s
test (ubuntu, 3.11, ~=1.1.0)	2m 35s
test (ubuntu, 3.11, @git+https://github.com/mesonbuild/meson.git)	2m 56s
test (windows, 3.11, @git+https://github.com/mesonbuild/meson.git)	4m 33s
mypy	13s
	1h 22m 42s

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