Set miriflags once for whole miri job

Author: dtolnay

.github/workflows/ci.yml

@@ -73,17 +73,15 @@ jobs:
   miri:
     name: Miri
     runs-on: ubuntu-latest
+    env:
+      MIRIFLAGS: "-Zmiri-tag-raw-pointers"
     steps:
       - uses: actions/checkout@v2
       - uses: dtolnay/rust-toolchain@nightly
         with:
           components: miri
       - run: cargo miri test
-        env:
-          MIRIFLAGS: "-Zmiri-tag-raw-pointers"
       - run: cargo miri test --features preserve_order,float_roundtrip,arbitrary_precision,raw_value
-        env:
-          MIRIFLAGS: "-Zmiri-tag-raw-pointers"
 
   clippy:
     name: Clippy