[backports-release-1.11] Backport 7c81745 ("Mmap tests: refresh tempname to avoid windows fs slowness") to Julia 1.11.x

[DilumAluthge]

Cherry picked from commit 7c81745, which was part of #57686.

Targets backports-release-1.11 (#59336).

Motivation

I'm hoping that this fixes the test failures in Windows CI (in the Mmap tests) that I'm seeing on backports-release-1.11.

Details

#58998 included a new test in the Mmap tests.

#58998 is now on the backports-release-1.11 branch.

CI is failing on the backports-release-1.11 branch (#59336), with a test failure in the Mmap tests, that looks like this:

Error in testset Mmap:
Error During Test at C:\buildkite-agent\builds\win2k22-amdci6-1\julialang\julia-release-1-dot-11\julia-ddcbe4dd84\share\julia\stdlib\v1.11\Mmap\test\runtests.jl:344
  Got exception outside of a @test
  IOError: unlink("C:\\Users\\julia\\AppData\\Local\\Temp\\jl_7Yt6Pgdm7K"): permission denied (EACCES)
  Stacktrace:

[DilumAluthge]

Hmmm. This does not seem to be sufficient.

[DilumAluthge]

I don't think this will work.

I think we should backport #59062 instead.