chore(onboarding): fix condition to enable SSI telemetry (#11101)

We noticed we weren't getting any telemetry

https://datadoghq.atlassian.net/browse/INPLAT-11

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lib-injection/sources/sitecustomize.py

@@ -33,7 +33,7 @@ def parse_version(version: str) -> Tuple:
 
 FORCE_INJECT = os.environ.get("DD_INJECT_FORCE", "").lower() in ("true", "1", "t")
 FORWARDER_EXECUTABLE = os.environ.get("DD_TELEMETRY_FORWARDER_PATH", "")
-TELEMETRY_ENABLED = "true" in os.environ.get("DD_INJECTION_ENABLED", "").lower()
+TELEMETRY_ENABLED = "DD_INJECTION_ENABLED" in os.environ
 DEBUG_MODE = os.environ.get("DD_TRACE_DEBUG", "").lower() in ("true", "1", "t")
 INSTALLED_PACKAGES = None
 PYTHON_VERSION = None