Add fillet on inside of head cover facemask

In the file [[HEAD-COVR-MIL1-COMN-01] Facemask.STL](https://github.com/input-inc/OpenSaint/blob/main/J5%20Project/Current%20CAD/3D%20Printable%20Parts/01%20-%20Head/00%20-%20Coverings/%5BHEAD-COVR-MIL1-COMN-01%5D%20Facemask.STL)

There's a sharp right angle on the inside vertical parts. It would be nice if it had a fillet there for strength. Mine broke immediately. 