async: Add feature(generic_associated_types)], fix CI

Author: Dirbaio

.github/workflows/clippy-async.yml

@@ -0,0 +1,19 @@
+on:
+  push:
+    branches: [ staging, trying, master ]
+  pull_request:
+
+name: Clippy check
+jobs:
+  clippy_check-async:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions-rs/toolchain@v1
+        with:
+          profile: minimal
+          toolchain: nightly
+          override: true
+          components: clippy
+      - run: cargo clippy
+        working-directory: embedded-hal-async

.github/workflows/clippy.yml

@@ -18,5 +18,3 @@ jobs:
       - uses: actions-rs/clippy-check@v1
         with:
           token: ${{ secrets.GITHUB_TOKEN }}
-      - run: cargo clippy
-        working-directory: embedded-hal-async

embedded-hal-async/src/lib.rs

@@ -9,3 +9,4 @@
 
 #![deny(missing_docs)]
 #![no_std]
+#![feature(generic_associated_types)]