translate tests: remove extra f in result report header

[romanc]

Description

Translate test report header currently prints an extra f before the backend name. Looks like an oversight from expanding the f-string. This PR fixes that.

How has this been tested?

As part of #465.

Checklist

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas: N/A
• I have made corresponding changes to the documentation (e.g. add new modules to docs/docstrings/): N/A
• My changes generate no new warnings
• Any dependent changes have been merged and published in downstream modules: N/A
• New check tests, if applicable, are included: N/A