FIX-#7461: Set backend correctly with environment variables. #16328

Job	Run time
python-filter	1s
execution-filter	5s
lint (flake8)	15s
Test API, headers and no-engine mode	17s
lint (mypy)	27s
test-internals	1s
test-clean-install-${{ matrix.os }}	1s
Test ${{ matrix.execution }} execution, Python ${{ needs.python-filter.outputs.python-version }}"	1s
test-${{ matrix.os }} (engine ${{ matrix.engine }}, python ${{ matrix.python-version }}, ${{ matrix.test_task }})	1s
test-ubuntu (engine unidist ${{ matrix.unidist-backend }}, python ${{ matrix.python-version }})	1s
test-asv-benchmarks	1s
test-${{ matrix.os }}-sanity (engine ${{ matrix.execution }}, python ${{ matrix.python-version }})	1s
test experimental	1s
test-spreadsheet (engine ${{ matrix.engine }}, python ${{ matrix.python-version }})	1s
test-native-dataframe-interoperability python ${{ matrix.python-version }})	1s
merge-coverage-artifacts	2s
upload-coverage	6s
	1m 23s

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