gh-151669: Normalize symlink targets in tarfile.TarFile.gettarinfo()

This applies a normalization complementary to the one added to
tarfile.TarFile.extract() in gh-138309.

Author: dnicolodi

Lib/tarfile.py

@@ -2227,7 +2227,7 @@ def gettarinfo(self, name=None, arcname=None, fileobj=None):
             type = FIFOTYPE
         elif stat.S_ISLNK(stmd):
             type = SYMTYPE
-            linkname = os.readlink(name)
+            linkname = os.readlink(name).replace(os.sep, "/")
         elif stat.S_ISCHR(stmd):
             type = CHRTYPE
         elif stat.S_ISBLK(stmd):