Fix race condition when starting several command tasks in quick succession

[stefanhaller]

• PR Description

Fixes #4507, see there for an elaborate description of the problem.

Labeled as ignore-for-release since this fixes a regression that was only introduced after the last release.

[codacy-production]

Coverage summary from Codacy

See diff coverage on Codacy

Coverage variation	Diff coverage
Report missing for 829aa3c1	✅ 100.00%

Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (829aa3c)	Report Missing	Report Missing	Report Missing
Head commit (3302a09)	55899	48502	86.77%

Coverage variation is the difference between the coverage for the head and common ancestor commits of the pull request branch: <coverage of head commit> - <coverage of common ancestor commit>

Diff coverage details

	Coverable lines	Covered lines	Diff coverage
Pull request (#4518)	2	2	100.00%

Diff coverage is the percentage of lines that are covered by tests out of the coverable lines that the pull request added or modified: <covered lines added or modified>/<coverable lines added or modified> * 100%

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Footnotes

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[stefanhaller]

This was approved privately on Discord by @jesseduffield, so I'm just going to merge this.