patch 9.1.2135: tests: tar plugin does not consider 'nowrapscan'

patch 9.1.2135: tests: tar plugin does not consider 'nowrapscan'

Problem:  search() is used to check for the message from tar that
          indicates leading slashes found in the tar archive, or to
          check for the leading slashes themselves. However, if
          'nowrapscan' is in effect these searches are limited to the
          last line and don't find any results. This causes the warning
          message from tar to be seen in the buffer, the "Path Traversal
          Attack Detected" message to be omitted, and editing actions
          can fail. This can be seen, for example, when editing
          src/testdir/samples/evil.tar.
Solution: Use the 'w' flag for search() (Kevin Goodsell)

closes: #19333

Signed-off-by: Kevin Goodsell <kevin-opensource@omegacrash.net>
Signed-off-by: Christian Brabandt <cb@256bit.org>