bpo-34542: Update test certs and keys (GH-8997) (GH-9007)

Update all test certs and keys to use future proof crypto settings:

* 3072 bit RSA keys
* SHA-256 signature

Signed-off-by: Christian Heimes <christian@python.org>
(cherry picked from commit e6dac0077996b1e1f886f036d6f2606237fa4c85)
20 files changed