ICPC: -diag-disable:conversion

Try to suppress the `-Werror-all` promotion in `#include <variant>`

Author: ax3l

.github/workflows/ci.yml

@@ -562,6 +562,7 @@ jobs:
     - name: Configure C++17
       run: |
         set +e; source /opt/intel/oneapi/setvars.sh; set -e
+        export CXXFLAGS="-diag-disable:conversion"
         cmake -S . -B build-17     \
         -DPYBIND11_WERROR=ON    \
         -DDOWNLOAD_CATCH=ON     \