ci: On nightly, use alternative stderr files for some tests

Works around dtolnay/trybuild#79

Author: meithecatte

.github/workflows/rust.yml

@@ -20,6 +20,9 @@ jobs:
         profile: minimal
         default: true
     - run: cargo build
+    - name: Prepare UI tests for nightly
+      if: matrix.rust == 'nightly'
+      run: for x in "test_suite/ui/*.nightly"; do cp "$x" "${x%.nightly}"; done
     - run: cargo test --all ${{ matrix.extra-test-opts }}
   clippy:
     runs-on: ubuntu-latest

test_suite/ui/multiple_bits_deferred.stderr.nightly

@@ -0,0 +1,10 @@
+error[E0277]: the trait bound `enumflags2::_internal::AssertionFailed: enumflags2::_internal::ExactlyOneBitSet` is not satisfied
+   --> $DIR/multiple_bits_deferred.rs:6:5
+    |
+6   |     Three = THREE,
+    |     ^^^^^^^^^^^^^ the trait `enumflags2::_internal::ExactlyOneBitSet` is not implemented for `enumflags2::_internal::AssertionFailed`
+    |
+   ::: $WORKSPACE/src/lib.rs:228:34
+    |
+228 |         where Assertion::Status: ExactlyOneBitSet {}
+    |                                  ---------------- required by this bound in `enumflags2::_internal::assert_exactly_one_bit_set`