[#1459] .golanci.yml: Add tenv linter, fix issues

Refs #1309

Signed-off-by: Evgenii Stratonikov <e.stratonikov@yadro.com>

.golangci.yml

@@ -88,5 +88,6 @@ linters:
     - testifylint
     - protogetter
     - intrange
+    - tenv
   disable-all: true
   fast: false

cmd/frostfs-node/config/test/config.go

@@ -11,8 +11,6 @@ import (
 )
 
 func fromFile(path string) *config.Config {
-	os.Clearenv() // ENVs have priority over config files, so we do this in tests
-
 	return config.New(path, "", "")
 }
 
@@ -40,15 +38,6 @@ func ForEachFileType(pref string, f func(*config.Config)) {
 
 // ForEnvFileType creates config from `<pref>.env` file.
 func ForEnvFileType(t testing.TB, pref string, f func(*config.Config)) {
-	envs := os.Environ()
-	t.Cleanup(func() {
-		os.Clearenv()
-		for _, env := range envs {
-			keyValue := strings.Split(env, "=")
-			os.Setenv(keyValue[0], keyValue[1])
-		}
-	})
-
 	f(fromEnvFile(t, pref+".env"))
 }
 
@@ -73,7 +62,6 @@ func loadEnv(t testing.TB, path string) {
 
 		v = strings.Trim(v, `"`)
 
-		err = os.Setenv(k, v)
+		t.Setenv(k, v)
-		require.NoError(t, err, "can't set environment variable")
 	}
 }