close metadata file after use in `importMetadata()`

warning message: 
```
..C:\repos\opencap-core\main.py:94: ResourceWarning: unclosed file <_io.TextIOWrapper name='C:\\repos\\opencap-core\\tests\\opencap-test-data\\Data\\sync-tests\\sessionMetadata.yaml' mode='r' encoding='cp1252'>
  sessionMetadata = importMetadata(os.path.join(sessionDir,
```