refactor: remove gotest.tools (#688)

* refactor: remove `gotest.tools`

* remove all references to `gotest.tools` and replace it with
  `github.com/stretchr/testify` which was originally used for tests
* bump `golangci-lint` version
* add `depguard` and `importas` to prevent import of unwanted packages
* add custom schema and information about config since
  schemastore.org has broken schema for `golangci-lint` config

* fix: handle more error cases

.github/workflows/checks.yml

@@ -16,7 +16,7 @@ jobs:
         env:
           CGO_ENABLED: 0
         with:
-          version: v1.39.0
+          version: v1.40.0
       - uses: github/super-linter@v3
         env:
           DEFAULT_BRANCH: master