Revert "..."

This reverts commit 2b3a812a9b759aa74b063cb21e0a16061879ff0b.

.github/workflows/ci.yml

@@ -31,7 +31,7 @@ jobs:
   rust-test:
     runs-on: ${{ matrix.os }}
 
-    continue-on-error: ${{ matrix.toolchain != 'stable' }}
+    continue-on-error: ${{ matrix.toolchain != stable }}
 
     strategy:
       matrix: