infra: fix typechecking of luthier by using `xpcall` instead of `pcall` #3510

Job	Run time
check-format	12s
lute-lint	2m 54s
build-docs-site	3m 5s
run-lute-cxx-unittests (windows-latest, --c-compiler cl.exe --cxx-compiler cl.exe)	4m 16s
run-lute-cxx-unittests (macos-latest, --enable-sanitizers)	5m 45s
run-lute-cxx-unittests (ubuntu-latest, --c-compiler gcc --cxx-compiler g++ --enable-sanitizers)	4m 30s
run-lute-cxx-unittests (ubuntu-latest, --c-compiler clang --cxx-compiler clang++ --enable-sanitiz...	4m 26s
run-lutecli-luau-tests (ubuntu-latest, --c-compiler gcc --cxx-compiler g++ --enable-sanitizers, t...	4s
lute-check	3m 45s
run-lutecli-luau-tests (windows-latest, --c-compiler cl.exe --cxx-compiler cl.exe, all)	4m 55s
run-lutecli-luau-tests (macos-latest, --enable-sanitizers, all)	5m 58s
run-lutecli-luau-tests (ubuntu-latest, --c-compiler clang --cxx-compiler clang++ --enable-sanitiz...	5m 14s
run-lutecli-luau-tests (ubuntu-latest, --c-compiler clang --cxx-compiler clang++ --enable-sanitiz...	4s
run-lutecli-luau-tests (ubuntu-latest, --c-compiler gcc --cxx-compiler g++ --enable-sanitizers, p...	5m 31s
Gated Commits	3s
	50m 42s

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