Add `--no-empty-msgstr` flag #949

Job	Run time
Build documentation	22s
Test (3.8, ubuntu-latest)	35s
Lint	4m 30s
Test (3.8, macos-latest)	1m 25s
Test (3.8, windows-latest)	1m 57s
Test (3.9, ubuntu-latest)	28s
Test (3.9, macos-latest)	23s
Test (3.9, windows-latest)	1m 27s
Test (3.10, ubuntu-latest)	37s
Test (3.10, macos-latest)	32s
Test (3.10, windows-latest)	1m 23s
Test (3.11, ubuntu-latest)	35s
Test (3.11, macos-latest)	31s
Test (3.11, windows-latest)	1m 55s
Build package	24s
Build standalone (ubuntu-latest)	1m 19s
Build standalone (macos-14)	44s
Build standalone (macos-13)	1m 25s
Build standalone (windows-latest)	1m 15s
Build final distribution	16s
Upload to PyPI	0s
Release	0s
	22m 3s

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