gh-141707: Fix tarfile type corruption with GNU long names

When processing GNU long name headers, the name field in the second
header contains garbage data. The V7 directory detection logic in
frombuf() would incorrectly mark regular files as directories if this
garbage ended with '/'. Re-apply the detection after patching the
actual long name to correct any type corruption.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: heathdutton

Lib/tarfile.py

@@ -1410,6 +1410,12 @@ def _proc_gnulong(self, tarfile):
         next.offset = self.offset
         if self.type == GNUTYPE_LONGNAME:
             next.name = nts(buf, tarfile.encoding, tarfile.errors)
+            # V7 directory detection in frombuf() may have used garbage
+            # name data. Re-apply it with the actual long name.
+            if next.type == DIRTYPE and not next.name.endswith("/"):
+                next.type = AREGTYPE
+            elif next.type == AREGTYPE and next.name.endswith("/"):
+                next.type = DIRTYPE
         elif self.type == GNUTYPE_LONGLINK:
             next.linkname = nts(buf, tarfile.encoding, tarfile.errors)