Alpine installation ignores Python 3.9

I'm trying to install BCC from the community repositories on Alpine with Python 3.9 installed.
Unfortunately, the installation ignores the existing python and installs Python 3.8 instead.

```
~ docker run -it --entrypoint=/bin/sh python:3.9-alpine
/ # apk update
fetch https://dl-cdn.alpinelinux.org/alpine/v3.13/main/x86_64/APKINDEX.tar.gz
fetch https://dl-cdn.alpinelinux.org/alpine/v3.13/community/x86_64/APKINDEX.tar.gz
v3.13.5-192-g9af04e1760 [https://dl-cdn.alpinelinux.org/alpine/v3.13/main]
v3.13.5-187-g1477654ee3 [https://dl-cdn.alpinelinux.org/alpine/v3.13/community]
OK: 13891 distinct packages available
/ # ln -s $(which python3) /usr/bin/python
/ # apk add bcc-tools bcc-doc
(1/9) Installing bcc-doc (0.18.0-r0)
(2/9) Installing fts (1.2.7-r1)
(3/9) Installing libelf (0.182-r0)
(4/9) Installing libgcc (10.2.1_pre1-r3)
(5/9) Installing libstdc++ (10.2.1_pre1-r3)
(6/9) Installing bcc (0.18.0-r0)
(7/9) Installing python3 (3.8.10-r0)
(8/9) Installing py3-bcc (0.18.0-r0)
(9/9) Installing bcc-tools (0.18.0-r0)
Executing busybox-1.32.1-r6.trigger
OK: 116 MiB in 45 packages
/ # python3.9
Python 3.9.4 (default, Apr 15 2021, 04:50:04)
[GCC 10.2.1 20201203] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import bcc
Traceback (most recent call last):
File "", line 1, in
ModuleNotFoundError: No module named 'bcc'
>>> exit()
/ # python3.8
Python 3.8.10 (default, May 6 2021, 00:05:59)
[GCC 10.2.1 20201203] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import bcc
>>> exit()
/ #
```

Reproduce the issue with the shown python:3.9-alpine Docker command and apk installation of bcc-tools and bcc-doc. Inspect how the Alpine packages select and install Python and py3-bcc; done means an existing Python 3.9 installation is used and `import bcc` succeeds there.

Written by the indexing model from the issue text.