Make TCRE diagnostic compatible with CMIP7 data

[schlunma]

Description

Addresses #647.

Checklist

Please confirm that this pull request has done the following:

• Tests added
• Documentation added (where applicable)
• Changelog item added to changelog/

[codecov]

Codecov Report

❌ Patch coverage is 80.00000% with 3 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...ool/src/climate_ref_esmvaltool/diagnostics/tcre.py	78.57%	1 Missing and 2 partials ⚠️

Flag	Coverage Δ
core	93.11% <ø> (ø)
providers	91.71% <80.00%> (-0.14%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
...ef-esmvaltool/src/climate_ref_esmvaltool/recipe.py	86.61% <100.00%> (ø)
...ool/src/climate_ref_esmvaltool/diagnostics/tcre.py	93.75% <78.57%> (-6.25%)	⬇️

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[schlunma]

After adding a series to this diagnostic it seems that one of the regressions tests is not failing even thought the expected series is empty...

[lewisjared]

Can you make an issue to capture that?

[schlunma]

See #703.