fix: enable and fixes rules from testifylint on test package

Signed-off-by: Matthieu MOREL <matthieu.morel35@gmail.com>

test/utils/ktesting/errorcontext_test.go

@@ -108,7 +108,7 @@ second error`,
 			assert.Equal(t, !tc.expectNoFail, tCtx.Failed(), "Failed()")
 			if tc.expectError == "" {
 				assert.NoError(t, err)
-			} else if assert.NotNil(t, err) {
+			} else if assert.Error(t, err) {
 				assert.Equal(t, tc.expectError, err.Error())
 			}
 		})