Fixed to use the right variable syntax (#3123)

Failed pipeline: Azure/azure-sdk-for-js#21216

https://dev.azure.com/azure-sdk/public/_build/results?buildId=1497101&view=logs&j=bc67675d-56bf-581f-e0a2-208848ba68ca&t=7eee3a58-6120-518b-7fcb-7e943712aa81

The test is based on move the variable out of if condition and check the syntax.

eng/common/pipelines/templates/steps/credscan.yml

@@ -30,14 +30,14 @@ steps:
   displayName: CredScan setup
 - task: securedevelopmentteam.vss-secure-development-tools.build-task-credscan.CredScan@3
   displayName: CredScan running
-  condition: and(succeededOrFailed(), ne('SKIP_CREDSCAN', true))
+  condition: and(succeededOrFailed(), ne(variables['SKIP_CREDSCAN'], true))
   inputs:
     toolVersion: 2.2.7.8 
     scanFolder: "${{ parameters.SourceDirectory }}/credscan.tsv"
     suppressionsFile: ${{ parameters.SuppressionFilePath }}
 - task: securedevelopmentteam.vss-secure-development-tools.build-task-postanalysis.PostAnalysis@2
   displayName: CredScan result analysis
-  condition: and(succeededOrFailed(), ne('SKIP_CREDSCAN', true))
+  condition: and(succeededOrFailed(), ne(variables['SKIP_CREDSCAN'], true))
   inputs:
     GdnBreakBaselineFiles: ${{ parameters.BaselineFilePath }}
     GdnBreakAllTools: false
@@ -50,4 +50,4 @@ steps:
 - pwsh: |
     Write-Host "Please check https://aka.ms/azsdk/credscan for more information about the cred scan failure."
   displayName: CredScan troubleshooting guide
-  condition: and(failed(), ne('SKIP_CREDSCAN', true))
+  condition: and(failed(), ne(variables['SKIP_CREDSCAN'], true))