meta-oniro-staging: Update python to 3.8.12

Python 3.8.12 is a security release, including a fix for
CVE-2021-29921.

From the official announcement [1]: Security content in this
release contains four fixes. There are also four additional
fixes for bugs that might have lead to denial-of-service attacks.

[1] https://www.python.org/downloads/release/python-3812/

Upstream-Status: Submitted [https://lists.openembedded.org/g/openembedded-core/message/158829

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Signed-off-by: Marta Rybczynska <marta.rybczynska@huawei.com>