specify custom brace style to fix unions

BreakBeforeBraces: Allman apparently includes all styles,
except for AfterUnion (which is false) when using clang-format -dump-config

Source/UnitTests/Common/BitFieldTest.cpp

@@ -7,7 +7,8 @@
 #include "Common/BitField.h"
 #include "Common/CommonTypes.h"
 
-union TestUnion {
+union TestUnion
+{
   u64 hex;
 
   BitField<0, 64, u64> full_u64;  // spans whole storage