tarfile: Extracting symlink using extractfile results in Keyerror: linkname not found

Bug report

Bug description:

I have the following tar archive containing some files and a symlink to a file that is not part of the tar archive.

drwxr-xr-x guif/users        0 2024-08-06 15:51 test/
-rw-r--r-- guif/users        0 2024-08-06 15:50 test/file3
lrwxrwxrwx guif/users        0 2024-08-06 15:51 test/mylink -> /usr/bin/env
-rw-r--r-- guif/users        0 2024-08-06 15:50 test/file1
-rw-r--r-- guif/users        0 2024-08-06 15:50 test/file2

I want to extract the symlink. With the getmember method I receive a valid member of the tar archive.
Using this member in the extractfile however results in an error.

#!/usr/bin/env python

import tarfile


def main():
    with tarfile.open('./test.tar') as tar_file:
        member = tar_file.getmember('test/mylink')
        file_content = tar_file.extractfile(member)


if __name__ == '__main__':
    main()

Traceback (most recent call last):
  File "/home/guif/repos/private/tmp/./main.py", line 13, in <module>
    main()
  File "/home/guif/repos/private/tmp/./main.py", line 9, in main
    file_content = tar_file.extractfile(member)
                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/nix/store/l014xp1qxdl6gim3zc0jv3mpxhbp346s-python3-3.12.4/lib/python3.12/tarfile.py", line 2385, in extractfile
    return self.extractfile(self._find_link_target(tarinfo))
                            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/nix/store/l014xp1qxdl6gim3zc0jv3mpxhbp346s-python3-3.12.4/lib/python3.12/tarfile.py", line 2725, in _find_link_target
    raise KeyError("linkname %r not found" % linkname)
KeyError: "linkname 'test//usr/bin/env' not found"

As you can see 'test//usr/bin/env can not be found.
The path does not look like the symlink I try to extract but more like <symlink name>/<link target>

From the doc:

Extract a member from the archive as a file object. `member' may be
a filename or a TarInfo object. If `member' is a regular file or
a link, an io.BufferedReader object is returned. For all other
existing members, None is returned. If `member' does not appear
in the archive, KeyError is raised.

CPython versions tested on:

3.10, 3.12

Operating systems tested on:

Linux

Lies tarfile.py im Umfeld von extractfile() und _find_link_target(), und führe anschließend das bereitgestellte Archiv und Skript aus, um den KeyError zu reproduzieren. Vergleiche das dokumentierte Verhalten für Links mit diesem Fall eines externen Ziels und füge Regressionstests hinzu, die das beabsichtigte Ergebnis eindeutig festlegen.