760: Bump minor version of heapless r=Dirbaio a=GrantM11235
Smoltcp uses `heapless::Vec::remove`, which was added in [version 0.7.15](https://github.com/japaric/heapless/blob/HEAD/CHANGELOG.md#v0715---2022-07-05)
There is also a newer version, [0.7.16](https://github.com/japaric/heapless/blob/HEAD/CHANGELOG.md#v0716---2022-08-09), but I don't know if smoltcp requires it
Co-authored-by: Grant Miller <GrantM11235@gmail.com>