lib: canonicalize regex whitebox test name

lib/regex/regex_test.ww

@@ -7,7 +7,7 @@
 // unexported internals (thread/newmatch, run_thread / add_thread /
 // delete_thread / search, find_last_groupstart / shift /
 // parse_repetition, is_consuming_inst) — lives in
-// lib/regex/regex_whitebox.ww (`package regex`, unified with regex.ww) and
+// lib/regex/whitebox_test.ww (`package regex`, unified with regex.ww) and
 // runs as a separate root-package binary.
 //
 // Fold 2a ports compile()'s lit/any/match arms only; exec lives in
@@ -26,7 +26,7 @@
 // name in struct-literal position (#29), and the imported EXPORTED type
 // is in scope unqualified. These reach only exported types — the #29
 // axis, distinct from the white-box privacy boundary handled by the
-// regex_whitebox.ww split above.
+// whitebox_test.ww split above.
 package regex_test;
 
 import regex;