Fix test expectation for single digit days

See <#16747 (review)>.

Co-authored-by: Ayesh Karunaratne <ayesh@aye.sh>

Author: cmb69

tests/basic/build_date.phpt

@@ -5,4 +5,4 @@ PHP_BUILD_DATE
 var_dump(PHP_BUILD_DATE);
 ?>
 --EXPECTREGEX--
-string\(20\) "[A-Za-z]{3} \d{2} \d{4} \d{2}:\d{2}:\d{2}"
+string\(20\) "[A-Za-z]{3} ( \d|\d{2}) \d{4} \d{2}:\d{2}:\d{2}"