add -Zmiri-disable-isolation to miri test

Author: ciehanski

.github/workflows/safety.yml

@@ -56,6 +56,7 @@ jobs:
           components: miri
 
       - name: cargo miri test
-        run: cargo miri test -Zmiri-disable-isolation
+        run: cargo miri test
         env:
+          RUSTFLAGS: "-Zmiri-disable-isolation"
           MIRIFLAGS: ""