fix(updater): Convert shell commands to PowerShell in workflow checkout step

The workflow was failing because it used shell syntax (bash) in a PowerShell context.
Converted the shell commands to proper PowerShell equivalents:
- Variable assignment using PowerShell syntax
- mkdir -> New-Item with -Force flag
- cd -> Set-Location
- regex replacement using PowerShell -replace operator

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: vaind

.github/workflows/updater.yml

@@ -137,12 +137,12 @@ jobs:
         #       Follow https://github.com/actions/checkout/issues/197
         run: |
           # Extract the ref from GITHUB_WORKFLOW_REF (e.g., getsentry/github-workflows/.github/workflows/updater.yml@refs/pull/109/merge -> refs/pull/109/merge)
-          WORKFLOW_REF=$(echo "${{ github.workflow_ref }}" | sed 's/.*@//')
-          mkdir -p ${{ runner.temp }}/ghwf
-          cd ${{ runner.temp }}/ghwf
+          $workflowRef = '${{ github.workflow_ref }}' -replace '.*@', ''
+          New-Item -ItemType Directory -Force -Path '${{ runner.temp }}/ghwf'
+          Set-Location '${{ runner.temp }}/ghwf'
           git init
           git remote add origin https://github.com/getsentry/github-workflows.git
-          git fetch --depth 1 origin ${WORKFLOW_REF}
+          git fetch --depth 1 origin $workflowRef
           git checkout FETCH_HEAD
 
       - name: Update to the latest version