configure.py: reenable -Wnarrowing

it seems that the tree builds just fine with this warning enabled.
and narrowing is a potentially unsafe numeric conversion. so let's
enable this warning option.

this change also helps to reduce the difference between the rules
generated by configure.py and those generated by CMake.

Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>

Closes scylladb/scylladb#16929

configure.py

@@ -1536,7 +1536,6 @@ def get_warning_options(cxx):
         '-Wno-unsupported-friend',
         # https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77728
         '-Wno-psabi',
-        '-Wno-narrowing',
         '-Wno-enum-constexpr-conversion',
     ]