gpx parse fix

[coolmule0]

Importing a gpx file does not work unless the file has a read attribute when using parse

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As a side not I am using Owntracks in its own instance, exporting using ocat, and importing into this timeline. One issue is that owntracks exports .gpx files with single quotes ' in the schema, while gpxpy expects the file to have double quotes ". See https://github.com/tkrajina/gpxpy/blob/cb243b22841bd2ce9e603fe3a96672fc75edecf2/gpxpy/parser.py#L105. I'm not if one of the two repos isn't following the schema properly. It means I need to manually adjust single quotes to double during the export/import process