[3.8] Fix typos in docs, comments and test assert messages (GH-14872). (#14900)

(cherry picked from commit 96e12d5f4f3c5a20986566038ee763dff3c228a1)

Co-authored-by: Min ho Kim <minho42@gmail.com>
diff --git a/Lib/email/headerregistry.py b/Lib/email/headerregistry.py
index 452c6ad..8d1a202 100644
--- a/Lib/email/headerregistry.py
+++ b/Lib/email/headerregistry.py
@@ -245,7 +245,7 @@
         the header name and the ': ' separator.
 
         """
-        # At some point we need to put fws here iif it was in the source.
+        # At some point we need to put fws here if it was in the source.
         header = parser.Header([
             parser.HeaderLabel([
                 parser.ValueTerminal(self.name, 'header-name'),