ci: fix no_std ci

.github/workflows/ci.yml

@@ -54,12 +54,6 @@ jobs:
         command:  check
         args: --no-default-features --features std
 
-    - name: check no_std
-      uses: actions-rs/cargo@v1
-      with:
-        command:  check
-        args: --no-default-features --features alloc
-
     - name: check attributes
       uses: actions-rs/cargo@v1
       with:
@@ -78,6 +72,22 @@ jobs:
         command: test
         args: --doc --features "unstable attributes"
 
+  build__with_no_std:
+    name: Build with no-std
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@master
+
+    - name: setup
+      run: rustup target add thumbv7m-none-eabi
+
+    - name: check no_std
+      uses: actions-rs/cargo@v1
+      with:
+        command:  check
+        args: --no-default-features --features alloc --target thumbv7m-none-eabi -v
+
   check_fmt_and_docs:
     name: Checking fmt and docs
     runs-on: ubuntu-latest