gh-143732: allow dict subclasses to be specialized #2625

Job	Run time
aarch64-apple-darwin/clang	8m 53s
x86_64-unknown-linux-gnu/gcc-free-threading	8m 19s
aarch64-unknown-linux-gnu/gcc	7m 7s
x86_64-apple-darwin/clang	22m 37s
x86_64-unknown-linux-gnu/gcc	9m 55s
	56m 51s

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