Fix error message in dotvvm.formatString date parsing #2751

Job	Run time
Build all projects without errors	10m 59s
.NET unit tests (ubuntu-latest)	3m 7s
.NET unit tests (windows-2022)	11m 35s
.NET unit tests (macOS-latest)	5m 0s
JS unit tests	2m 19s
Build published projects without warnings (Release)	3m 0s
Build published projects without warnings (Debug)	4m 14s
UI tests (chrome, ubuntu-latest, Production, Default)	17m 18s
UI tests (chrome, windows-2022, Development, Default)	23m 30s
UI tests (firefox, ubuntu-latest, Development, Default)	21m 25s
UI tests (firefox, ubuntu-latest, Production, Default)	20m 6s
UI tests (firefox, ubuntu-latest, Development, ExperimentalFeaturesTests)	21m 29s
UI tests (chrome, ubuntu-latest, Production, ExperimentalFeaturesTests)	13m 17s
	2h 37m 19s

Provide feedback