style: Fixes unnecessary-collection-call (C408) for testsuite

[echoix]

Only applies fixes to non-empty collections by ruff check --select "C408" --unsafe-fixes --output-format=concise --fix --config 'include = ["*/testsuite/**.py"]' in order to limit the review scope.

Continuation of #3945, but for fixes that aren't empty collections and only in the testsuite folders, in order to separate it from other changes. Part of the effort to introduce Pylint 3.x for https://github.com/OSGeo/grass/issues/3921

Uses the fixes provided for ruff rule unnecessary-collection-call (C408) to fix part of Pylint's use-dict-literal / R1735 rule.