chore: update to use spdx license identifier #1507

Job	Run time
cargo-c	10s
Clang Tidy	12s
Build+test (clang, stable, ubuntu-latest)	59s
Build+test (clang, beta, ubuntu-latest)	1m 4s
Clippy	12s
Clippy nightly (optional)	18s
Build+test (clang, nightly, ubuntu-latest)	1m 9s
Build+test (clang, 1.64.0, ubuntu-latest)	2m 25s
Check for documentation errors	17s
Build+test (gcc, stable, ubuntu-latest)	57s
ensure-header-updated	1m 20s
Build+test (gcc, beta, ubuntu-latest)	1m 6s
Format	12s
Build+test (gcc, nightly, ubuntu-latest)	58s
Check minimum versions	42s
Build+test (gcc, 1.64.0, ubuntu-latest)	2m 15s
Build+test (macos-latest, clang, stable)	1m 4s
Miri	1m 10s
Windows CMake, Debug configuration	1m 45s
Windows CMake, Release configuration	2m 30s
Valgrind	1m 32s
	22m 17s

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