When marshaling the type with `gopkg.in/yaml.v3`, unmarshaling would
recursively call the type's `MarshalYAML()` function, which ultimately
resulted in a crash:
runtime: goroutine stack exceeds 1000000000-byte limit
runtime: sp=0x140202e0430 stack=[0x140202e0000, 0x140402e0000]
fatal error: stack overflow
This applies a similar fix as was implemented in e7788d6f9a
for the `MarshalJSON()` implementation. An alternative would be to use
a type alias (to remove the `MarshalYAML()`), but keeping it simple.
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
0644aa3906