[#146] Fix preconditions: trim quotes in etags

Signed-off-by: Denis Kirillov <d.kirillov@yadro.com>

api/handler/get_test.go

@@ -2,6 +2,7 @@ package handler
 
 import (
 	"bytes"
+	stderrors "errors"
 	"fmt"
 	"io"
 	"net/http"
@@ -149,7 +150,11 @@ func TestPreconditions(t *testing.T) {
 	} {
 		t.Run(tc.name, func(t *testing.T) {
 			actual := checkPreconditions(tc.info, tc.args)
-			require.Equal(t, tc.expected, actual)
+			if tc.expected == nil {
+				require.NoError(t, actual)
+			} else {
+				require.True(t, stderrors.Is(actual, tc.expected), tc.expected, actual)
+			}
 		})
 	}
 }