ci: Temporarily disable aarch64_be test

rust-lang/rust#132714 bumped memchr without
considering aarch64_be is not supported in memchr:
BurntSushi/memchr#162

Author: taiki-e

.github/workflows/ci.yml

@@ -52,7 +52,8 @@ jobs:
           # rustc --print target-list | grep -e '-linux-gnu'
           - aarch64-unknown-linux-gnu
           # - aarch64-unknown-linux-gnu_ilp32 # tier3
-          - aarch64_be-unknown-linux-gnu # tier3
+          # TODO: https://github.com/BurntSushi/memchr/pull/162
+          # - aarch64_be-unknown-linux-gnu # tier3
           # - aarch64_be-unknown-linux-gnu_ilp32 # tier3
           - arm-unknown-linux-gnueabi
           # - arm-unknown-linux-gnueabihf # supported in rust-cross-toolchain but not ported to this action