Use simple match instead of regex match in GCE Windows OpenSSH startup script

[mauriciopoppe]

/kind bug

What this PR does / why we need it:

Followup of #106196, the good news is that the SSH issue is fixed! Prow could SSH to the Windows VM however after checking the contents of the administrators_keys_file I saw that it was increasing in size for every run of the loop, this is because of these new lines:

      $found = Select-String -Path $user_keys_file -Pattern $ssh_key
      if ($found -eq $null) {
        Add-Content -Encoding UTF8 $user_keys_file $ssh_key
      }
      $found = Select-String -Path $administrator_keys_file -Pattern $ssh_key
      if ($found -eq $null) {
        Add-Content -Encoding UTF8 $administrator_keys_file $ssh_key
      }

Select-String is using regex by default and the pattern contains some characters that are interpreted differently if they're part of a regex expression and therefore a key would never be found and it'd be appended to the file even if the string was there, I saw that -SimpleMatch fixes it.

Does this PR introduce a user-facing change?

NONE

/cc @pjh
/sig windows

[mauriciopoppe]

/cc @ibabou
hey Ibrahim, please take a look if you get the chance, thanks in advance :)

[pjh]

/priority important-soon
/triage accepted

[pjh]

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: mauriciopoppe, pjh

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• cluster/gce/windows/OWNERS [pjh]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment