fix golangci-lint(depguard) errors

[demouth]

Add depguard setting to the linters-settings of the .golangci.yml file to fix the following errors that occur in the Run Tests workflow.

Error: import 'github.com/gin-gonic/gin' is not allowed from list 'Main' (depguard)
Error: import 'github.com/gin-gonic/gin' is not allowed from list 'Main' (depguard)
Error: import 'github.com/gin-gonic/gin' is not allowed from list 'Main' (depguard)
Error: import 'github.com/stretchr/testify/assert' is not allowed from list 'Main' (depguard)
Error: import 'github.com/stretchr/testify/assert' is not allowed from list 'Main' (depguard)
Error: import 'github.com/stretchr/testify/assert' is not allowed from list 'Main' (depguard)