/usr/lib/mysql-testsuite/std_data/server-key.pem is in mysql-testsuite-5.6 5.6.16-1~exp1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 | -----BEGIN RSA PRIVATE KEY-----
MIIBOwIBAAJBAM3kh1GdchGg0frzkosTHOv34povcqjWZUjRaa8bwEwT5WBgUUHp
q6a8E7sMXjJ82WyezQUkhHjbgJEu2Igrwu0CAwEAAQJBAJuwhFbF3NzRpBbEmnqJ
4GPa1UJMQMLFJF+04tqj/HxJcAIVhOJhGmmtYNw1yjz/ZsPnfJCMz4eFOtdjvGtf
peECIQDmFFg2WLvYo+2m9w9V7z4ZIkg7ixYkI/ObUUctfZkPOQIhAOUWnrvjFrAX
bIvYT/YR50+3ZDLEc51XxNgJnWqWYl1VAiEAnTOFWgyivFC1DgF8PvDp8u5TgCt2
A1d1GMgd490O+TECIC/WMl0/hTxOF9930vKqOGf//o9PUGkZq8QE9fcM4gtlAiAE
iOcFpnLjtWj57jrhuw214ucnB5rklkQQe+AtcARNkg==
-----END RSA PRIVATE KEY-----
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