Issue #27076: Doc, comment and tests spelling fixes

Most fixes to Doc/ and Lib/ directories by Ville Skyttä.
diff --git a/Python/fileutils.c b/Python/fileutils.c
index 8987ce5..23eed71 100644
--- a/Python/fileutils.c
+++ b/Python/fileutils.c
@@ -176,7 +176,7 @@
 #endif
 
 error:
-    /* if an error occured, force the ASCII encoding */
+    /* if an error occurred, force the ASCII encoding */
     return 1;
 }