Upgrade cspell packages to version ^6.12.0 (Azure#19405)

to address dependabot issue https://github.com/Azure/azure-sdk-for-js/security/dependabot/13

Co-authored-by: Jeremy Meng <yumeng@microsoft.com>

Author: azure-sdk

eng/common/spelling/Invoke-Cspell.ps1

@@ -84,7 +84,7 @@ if (!(Test-Path $CSpellConfigPath)) {
 
 function Test-VersionReportMatches() {
   # Arrange
-  $expectedPackageVersion = '5.12.3'
+  $expectedPackageVersion = '6.12.0'
 
   # Act
   $actual = &"$PSSCriptRoot/Invoke-Cspell.ps1" `