tags.subset can miss the relevant tags

[dabreegster]

Way 893136312 produces the error Conversion Error: unsupported: 'lane count mismatch' - 'no tags' - osm2lanes/src/transform/tags_to_lanes/modes/bus/mod.rs:154:28

The way in question has bus:lanes:forward, but not bus:lanes. We should consider including all tags with the prefix, since that's often how tag keys get used