package/python3: bump to version 3.8.6

package/python3: bump to version 3.8.6

Contains a number of bugfixes. For details, see the changelog:

https://docs.python.org/release/3.8.6/whatsnew/changelog.html#changelog

Update the license hash for the addition of a note stating that the examples
and documentation is now dual licensed under the PSF and a Zero-Clause BSD
license since:

https://github.com/python/cpython/commit/9fef7c54a0adfade5ec94259d97f22e05fe9e3e3

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>