Go pipeline creation fails when YAML filename has no variant

## Description

Go pipeline creation fails because the pipeline YAML filename does not include a variant.

## Error

```text
PipelineGenerator.Program[0]
Suggested fix: add a 'variant' to the yaml filename, e.g. 'sdk/keyvault/internal/ci.yml' => 'sdk/keyvault/internal/ci.keyvault.yml'
```

## Run log

https://dev.azure.com/azure-sdk/internal/_build/results?buildId=6828578&view=logs&s=96ac2280-8cb4-5df5-99de-dd2da759617d&j=011e1ec8-6569-5e69-4f06-baf193d1351e