[msh2vtu] When invoked from the shell filename arg is a string.

Required for ogs/ogs!5222 (merged).

changed milestone to %0.6.0 Release

added workflowplease review label

requested review from @TobiasMeisel

added BugFix label

assigned to @bilke

approved this merge request

mentioned in commit FZill/ogs@f5c9e59d

enabled an automatic merge when all merge checks for 1163ed8c pass

mentioned in commit 8fdcb330

merged