fix(shell/pwsh): use empty string for CONDA_PROMPT_MODIFIER

Assigning \False stringifies to the literal False, which passes
conda's own truthiness check and gets Write-Host'ed on every prompt.
An empty string matches what conda's prompt wrapper actually expects.

Fixes #7733

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
Entire-Checkpoint: ce0acf0d99c9

src/shell/scripts/omp.ps1

@@ -159,7 +159,7 @@ New-Module -Name "oh-my-posh-core" -ScriptBlock {
     $env:POWERLINE_COMMAND = "oh-my-posh"
     $env:POSH_SHELL = "pwsh"
     $env:POSH_SHELL_VERSION = $script:PSVersion
-    $env:CONDA_PROMPT_MODIFIER = $false
+    $env:CONDA_PROMPT_MODIFIER = ''
 
     function Invoke-Utf8Posh {
         param([string[]]$Arguments = @())