Your commit statement misses the 'branchName' argument.
.then(workingCopy => workingCopy.commit())
The commit is not automatically done on the branch from which you created your working copy.
From the Platform SDK documentation:
commit(branchName?: string, baseRevision?: number): Promise<Revision>
Parameters
Optional branchName: string
(Optional) the branch to commit to. Use null for main line.
Optional baseRevision: number
(Optional) the base revision of this commit.
This is also not working in Mendix 7.2.0. Anybody?