[Eng] Fix pattern in when matching *.Autorest (#28059)

Author: VeryEarly

tools/BuildScripts/AdaptAutorestModule.ps1

@@ -50,7 +50,7 @@ if ($ModuleRootName -in $rootToParentMap.keys) {
 
 $moduleRootPath = Join-Path $SourceDirectory $ModuleRootName
 $subModuleNameTrimmed = $SubModuleName
-$subModuleName = Get-ChildItem -Path $moduleRootPath -Directory | Where-Object { $_.Name -match '$(subModuleNameTrimmed)\.' } | ForEach-Object { $_.Name }
+$subModuleName = Get-ChildItem -Path $moduleRootPath -Directory | Where-Object { $_.Name -match "${subModuleNameTrimmed}\." } | ForEach-Object { $_.Name }
 
 $parentModulePath = Join-Path $moduleRootPath $parentModuleName
 $subModulePath = Join-Path $moduleRootPath $SubModuleName
@@ -274,4 +274,4 @@ New-GenerateInfoJson -GeneratedDirectory $subModulePath
 <#
     Update module in tools\CreateMappings_rules.json
 #>
-Update-MappingJson -RepoRoot $RepoRoot -ModuleName $ModuleRootName
+Update-MappingJson -RepoRoot $RepoRoot -ModuleName $ModuleRootName