Temporarily disable aarch64_be test due to core_simd bug

rust-lang/portable-simd#348

```
error[E0432]: unresolved imports `core::arch::aarch64::vqtbl1q_u8`, `core::arch::aarch64::vtbl1_u8`
  --> /home/runner/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/../../portable-simd/crates/core_simd/src/swizzle_dyn.rs:20:46
    |
 20 |         use core::arch::aarch64::{uint8x8_t, vqtbl1q_u8, vtbl1_u8};
    |                                              ^^^^^^^^^^  ^^^^^^^^ no `vtbl1_u8` in `core_arch::arch::aarch64`
    |                                              |
    |                                              no `vqtbl1q_u8` in `core_arch::arch::aarch64`
    |
 help: a similar name exists in the module
    |
 20 |         use core::arch::aarch64::{uint8x8_t, vst1q_u8, vtbl1_u8};
    |                                              ~~~~~~~~
 help: a similar name exists in the module
    |
 20 |         use core::arch::aarch64::{uint8x8_t, vqtbl1q_u8, vtrn1_u8};
    |                                                          ~~~~~~~~
```

Author: taiki-e

.github/workflows/ci.yml

@@ -64,8 +64,9 @@ jobs:
             target: aarch64-unknown-linux-gnu
           - rust: nightly
             target: aarch64-unknown-linux-gnu
-          - rust: nightly
-            target: aarch64_be-unknown-linux-gnu
+          # TODO: core_simd bug https://github.com/rust-lang/portable-simd/pull/348
+          # - rust: nightly
+          #   target: aarch64_be-unknown-linux-gnu
           - rust: stable
             target: arm-unknown-linux-gnueabi
           - rust: nightly

tools/build.sh

@@ -30,11 +30,13 @@ default_targets=(
     # rustc --print target-list | grep -E '^(aarch64|arm64)'
     aarch64-unknown-linux-gnu
     # aarch64 big endian
-    aarch64_be-unknown-linux-gnu
+    # TODO: core_simd bug https://github.com/rust-lang/portable-simd/pull/348
+    # aarch64_be-unknown-linux-gnu
     # aarch64 ILP32 ABI
     aarch64-unknown-linux-gnu_ilp32
     # aarch64 ILP32 ABI big endian
-    aarch64_be-unknown-linux-gnu_ilp32
+    # TODO: core_simd bug https://github.com/rust-lang/portable-simd/pull/348
+    # aarch64_be-unknown-linux-gnu_ilp32
     # aarch64 always support lse
     aarch64-apple-darwin