Adapt dependency of mpz to new repo location #927

Job	Run time
build_and_test (components/integration-tests)	2m 35s
build_and_test (components/uid-mux)	59s
build_and_test (components/actors/actor-ot)	1m 41s
build_and_test (components/cipher)	2m 26s
build_and_test (components/universal-hash)	3m 1s
build_and_test (components/aead)	2m 33s
build_and_test (components/key-exchange)	2m 57s
build_and_test (components/point-addition)	1m 55s
build_and_test (components/prf)	2m 45s
build_and_test (components/tls)	2m 38s
build_and_test (tlsn)	5m 15s
	28m 45s

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