Add `--no-empty-msgstr` flag #950

Job	Run time
Lint	4m 21s
Build documentation	28s
Test (3.8, ubuntu-latest)	39s
Test (3.8, macos-latest)	1m 26s
Test (3.8, windows-latest)	1m 20s
Test (3.9, ubuntu-latest)	37s
Test (3.9, macos-latest)	29s
Test (3.9, windows-latest)	1m 10s
Test (3.10, ubuntu-latest)	32s
Test (3.10, macos-latest)	41s
Test (3.10, windows-latest)	1m 21s
Test (3.11, ubuntu-latest)	33s
Test (3.11, macos-latest)	49s
Test (3.11, windows-latest)	1m 32s
Build package	13s
Build standalone (ubuntu-latest)	1m 22s
Build standalone (macos-14)	33s
Build standalone (macos-13)	1m 3s
Build standalone (windows-latest)	1m 33s
Build final distribution	17s
Upload to PyPI	0s
Release	0s
	20m 59s

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