Merge ElementsProject/rust-secp256k1-zkp#81: Update vendored version … #301

Job	Run time
Nightly - ASan + Bench + Docs	1m 12s
WASM (stable)	49s
Release tests with global context enabled (1.56.1, ubuntu-latest)	1m 58s
WASM (beta)	56s
Tests (1.56.1, ubuntu-latest)	3m 7s
Release tests with global context enabled (beta, ubuntu-latest)	27s
WASM (nightly)	54s
Release tests with global context enabled (beta, macos-latest)	27s
Tests (beta, ubuntu-latest)	1m 17s
Tests (beta, macos-latest)	1m 13s
Release tests with global context enabled (stable, ubuntu-latest)	16s
Release tests with global context enabled (stable, macos-latest)	22s
Tests (stable, ubuntu-latest)	1m 9s
Tests (stable, macos-latest)	53s
	15m 0s

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