Merge #597: CI: Pin memchr

3d1793a CI: Pin memchr (Tobin C. Harding)

Pull request description:

  Recently `memchr` broke our MSRV by updating to edition 2021 in a patch version, pin it in CI for MSRV builds.

ACKs for top commit:
  apoelstra:
    ACK 3d1793a

Tree-SHA512: cb7c6876bcb0cd16deb29e34240b9628b5aad39eb7a6ca4943b8d01c2f03b324e6166fd63c628bf1acbd9db1be90e7924a25fd5d3ec0ab82aabce1b96429462b

Author: apoelstra

contrib/test.sh

@@ -29,6 +29,7 @@ if cargo --version | grep "1\.48\.0"; then
     cargo update -p serde --precise 1.0.152
     cargo update -p log --precise 0.4.18
     cargo update -p serde_test --precise 1.0.152
+    cargo update -p memchr --precise 2.5.0
 fi
 
 # Test bitcoind integration tests if told to (this only works with the stable toolchain)