feat: update .gitignore to exclude generated api reference files #1

Job	Run time
std::format none C++20 Clang-18 Release	6m 39s
std::format none C++20 Clang-18 Debug	6m 13s
std::format none C++23 Clang-18 Release	6m 17s
std::format none C++23 Clang-18 Debug	5m 59s
std::format gsl-lite C++20 Clang-18 Release	6m 47s
std::format gsl-lite C++20 Clang-18 Debug	6m 20s
std::format gsl-lite C++23 Clang-18 Release	6m 22s
std::format gsl-lite C++23 Clang-18 Debug	6m 5s
std::format ms-gsl C++20 Clang-18 Release	6m 37s
std::format ms-gsl C++20 Clang-18 Debug	6m 25s
std::format ms-gsl C++23 Clang-18 Release	6m 33s
std::format ms-gsl C++23 Clang-18 Debug	6m 10s
fmtlib none C++20 Clang-18 Release	6m 44s
fmtlib none C++20 Clang-18 Debug	6m 12s
fmtlib none C++23 Clang-18 Release	6m 27s
fmtlib none C++23 Clang-18 Debug	6m 1s
fmtlib gsl-lite C++20 Clang-18 Release	6m 35s
fmtlib gsl-lite C++20 Clang-18 Debug	6m 31s
fmtlib gsl-lite C++23 Clang-18 Release	6m 21s
fmtlib gsl-lite C++23 Clang-18 Debug	6m 7s
fmtlib ms-gsl C++20 Clang-18 Release	6m 35s
fmtlib ms-gsl C++20 Clang-18 Debug	6m 18s
fmtlib ms-gsl C++23 Clang-18 Release	6m 33s
fmtlib ms-gsl C++23 Clang-18 Debug	6m 11s
	2h 33m 2s

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