pythongh-127794: Coverge all the validations into a single regex

Author: srinivasreddy

Lib/email/_policybase.py

@@ -92,7 +92,8 @@ def __add__(self, other):
 
 def validate_header(name, value):
     # Validate header name according to RFC 5322
-    if not name or ' ' in name or '\t' in name or ':' in name:
+    import re
+    if not re.match(r'^[^\s:]+$', name):
         raise ValueError(f"Invalid header field name {name!r}")
     # Only allow printable ASCII characters
     if any(ord(c) < 33 or ord(c) > 126 for c in name):