sync: sort .mailmap independently of the locale

mailmap-update.sh sorts .mailmap with the caller's locale collation, so
the order of its entries depends on who runs the sync: e.g., with
en_US.UTF-8 vs C.UTF-8 (the default on GitHub runners). Syncs done in
different environments would keep reordering the file.

Always sort with LC_ALL=C.

Assisted-by: Claude:claude-opus-5-5
Signed-off-by: Ihor Solodrai <ihor.solodrai@linux.dev>

scripts/mailmap-update.sh

@@ -34,4 +34,5 @@ while read -r email; do
     grep_lines "${email}$" "${LINUX_MAILMAP}" >> "${tmpfile}"
 done < <(git log --format='<%ae>' | sort -u)
 
-sort -u "${tmpfile}" > "${LIBBPF_MAILMAP}"
+# Sort independently of the locale, for the result not to depend on who runs it
+LC_ALL=C sort -u "${tmpfile}" > "${LIBBPF_MAILMAP}"