Fix integration test runner

Author: flip1995

.github/workflows/clippy_bors.yml

@@ -223,7 +223,6 @@ jobs:
       run: $CARGO_TARGET_DIR/debug/integration
       env:
         INTEGRATION: ${{ matrix.integration }}
-        RUSTUP_TOOLCHAIN: master
 
   # These jobs doesn't actually test anything, but they're only used to tell
   # bors the build completed, as there is no practical way to detect when a