[connector/datadog] Fix go directive (open-telemetry#26356)

**Description:** <Describe what has changed.>
<!--Ex. Fixing a bug - Describe the bug and how this fixes the issue.
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The `go` directive was pointing to Go 1.19 instead of Go 1.20.

connector/datadogconnector/go.mod

@@ -1,6 +1,6 @@
 module github.com/open-telemetry/opentelemetry-collector-contrib/connector/datadogconnector
 
-go 1.19
+go 1.20
 
 require (
 	github.com/DataDog/datadog-agent/pkg/proto v0.48.0-beta.1