Fix tracing debug

[ukclivecox]

What this PR does / why we need it:

Ensures tracing is not activated if TRACING=0 in python wrapper.

Which issue(s) this PR fixes:

Fixes #3158

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

[review-notebook-app]

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[ukclivecox]

/test integration

[seldondev]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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[ukclivecox]

/test integration

[ukclivecox]

/test notebooks

[ukclivecox]

/test integration

[ukclivecox]

/test notebooks

[axsaucedo]

/test integration

[ukclivecox]

/test integration

[ukclivecox]

/test notebooks

[axsaucedo]

/test notebooks

[axsaucedo]

/test integration

[axsaucedo]

/test notebooks

[axsaucedo]

All tests seem to pass and no extra review comments - merging 👍

[seldondev]

@cliveseldon: The following test failed, say /retest to rerun them all:

Test name	Commit	Details	Rerun command
notebooks	e04cc2f	link	/test notebooks

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