[chore][mdatagen] Fix failed tests when there are no enabled events b… (open-telemetry#13121)

…y default

<!--Ex. Fixing a bug - Describe the bug and how this fixes the issue.
Ex. Adding a feature - Explain what this achieves.-->
#### Description
Sometimes, we want all events to be disabled by default, allowing users
to enable them manually. This approach can be helpful in such cases.

<!--Please delete paragraphs that you did not use before submitting.-->

Author: sincejune

cmd/mdatagen/internal/samplereceiver/internal/metadata/generated_logs_test.go

@@ -215,7 +215,7 @@ func TestLogsBuilder(t *testing.T) {
 			{{- end }}
 			logs := lb.Emit(WithLogsResource(res))
 
-			if tt.expectEmpty {
+			if tt.expectEmpty || ((tt.name == "default" || tt.name == "filter_set_include") && defaultEventsCount == 0) {
 				assert.Equal(t, 0, logs.ResourceLogs().Len())
 				return
 			}