bpo-34625: Update vendorized expat version to 2.2.6. (GH-9150)

(cherry picked from commit 5033aa77aacaa5505636f150e8d54baac5bdca9c)

Co-authored-by: Benjamin Peterson <benjamin@python.org>
diff --git a/Modules/expat/xmltok_impl.c b/Modules/expat/xmltok_impl.c
index 0403dd3..4d9ae7d 100644
--- a/Modules/expat/xmltok_impl.c
+++ b/Modules/expat/xmltok_impl.c
@@ -74,6 +74,7 @@
       *nextTokPtr = ptr; \
       return XML_TOK_INVALID; \
     } \
+    /* fall through */ \
   case BT_NMSTRT: \
   case BT_HEX: \
   case BT_DIGIT: \
@@ -102,6 +103,7 @@
       *nextTokPtr = ptr; \
       return XML_TOK_INVALID; \
     } \
+    /* fall through */ \
   case BT_NMSTRT: \
   case BT_HEX: \
     ptr += MINBPC(enc); \
@@ -602,7 +604,7 @@
           return XML_TOK_INVALID;
         }
       }
-    /* fall through */
+      /* fall through */
     case BT_EQUALS:
       {
         int open;
@@ -1442,6 +1444,7 @@
     case BT_NMSTRT:
       if (!(BYTE_TO_ASCII(enc, ptr) & ~0x7f))
         break;
+      /* fall through */
     default:
       switch (BYTE_TO_ASCII(enc, ptr)) {
       case 0x24: /* $ */
@@ -1659,8 +1662,8 @@
 {
   for (; *ptr2; ptr1 += MINBPC(enc), ptr2++) {
     if (end1 - ptr1 < MINBPC(enc)) {
-      /* This line cannot be executed.  THe incoming data has already
-       * been tokenized once, so imcomplete characters like this have
+      /* This line cannot be executed.  The incoming data has already
+       * been tokenized once, so incomplete characters like this have
        * already been eliminated from the input.  Retaining the
        * paranoia check is still valuable, however.
        */