[chore]: enable len and empty rules from testifylint (#5832)

#### Description

Testifylint is a linter that provides best practices with the use of
testify.

This PR enables
[empty](https://github.com/Antonboom/testifylint?tab=readme-ov-file#empty)
and
[len](https://github.com/Antonboom/testifylint?tab=readme-ov-file#len)
rules from [testifylint](https://github.com/Antonboom/testifylint)

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

sdk/metric/pipeline_test.go

@@ -45,7 +45,7 @@ func TestNewPipeline(t *testing.T) {
 	err := pipe.produce(context.Background(), &output)
 	require.NoError(t, err)
 	assert.Equal(t, resource.Empty(), output.Resource)
-	assert.Len(t, output.ScopeMetrics, 0)
+	assert.Empty(t, output.ScopeMetrics)
 
 	iSync := instrumentSync{"name", "desc", "1", testSumAggregateOutput}
 	assert.NotPanics(t, func() {