Fix completion test baselines for --os option in restore command

Co-authored-by: marcpopMSFT <[email protected]>

Author: Copilot

test/dotnet.Tests/CompletionTests/snapshots/bash/DotnetCliSnapshotTests.VerifyCompletions.verified.sh

@@ -1310,7 +1310,7 @@ _testhost_restore() {
     prev="${COMP_WORDS[COMP_CWORD-1]}" 
     COMPREPLY=()
 
-    opts="--disable-build-servers --source --packages --use-current-runtime --disable-parallel --configfile --no-http-cache --ignore-failed-sources --force --runtime --no-dependencies --verbosity --interactive --artifacts-path --use-lock-file --locked-mode --lock-file-path --force-evaluate --arch --help" 
+    opts="--disable-build-servers --source --packages --use-current-runtime --disable-parallel --configfile --no-http-cache --ignore-failed-sources --force --runtime --no-dependencies --verbosity --interactive --artifacts-path --use-lock-file --locked-mode --lock-file-path --force-evaluate --arch --os --help" 
 
     if [[ $COMP_CWORD == "$1" ]]; then
         COMPREPLY=( $(compgen -W "$opts" -- "$cur") )

test/dotnet.Tests/CompletionTests/snapshots/pwsh/DotnetCliSnapshotTests.VerifyCompletions.verified.ps1

@@ -785,6 +785,7 @@ Register-ArgumentCompleter -Native -CommandName 'testhost' -ScriptBlock {
                 [CompletionResult]::new('--force-evaluate', '--force-evaluate', [CompletionResultType]::ParameterName, "Forces restore to reevaluate all dependencies even if a lock file already exists.")
                 [CompletionResult]::new('--arch', '--arch', [CompletionResultType]::ParameterName, "The target architecture.")
                 [CompletionResult]::new('--arch', '-a', [CompletionResultType]::ParameterName, "The target architecture.")
+                [CompletionResult]::new('--os', '--os', [CompletionResultType]::ParameterName, "The target operating system.")
                 [CompletionResult]::new('--help', '--help', [CompletionResultType]::ParameterName, "Show command line help.")
                 [CompletionResult]::new('--help', '-h', [CompletionResultType]::ParameterName, "Show command line help.")
             )

test/dotnet.Tests/CompletionTests/snapshots/zsh/DotnetCliSnapshotTests.VerifyCompletions.verified.zsh

@@ -813,6 +813,7 @@ _testhost() {
                         '--force-evaluate[Forces restore to reevaluate all dependencies even if a lock file already exists.]' \
                         '--arch=[The target architecture.]:ARCH: ' \
                         '-a=[The target architecture.]:ARCH: ' \
+                        '--os=[The target operating system.]:OS: ' \
                         '--help[Show command line help.]' \
                         '-h[Show command line help.]' \
                         '*::PROJECT | SOLUTION | FILE -- The project or solution or C# (file-based program) file to operate on. If a file is not specified, the command will search the current directory for a project or solution.: ' \