MDEV-23662: Make S3 Storage Engine tests better

To ensure that S3 is using its access and secret
key in the right way, make these different in the test
suite.

mysql-test/suite/s3/my.cnf

@@ -19,7 +19,7 @@ s3-host-name="127.0.0.1"
 # Note: s3-host-name="localhost" doesn't work. It causes
 # libmarias3 to use the wrong variant of the protocol.
 s3-bucket=storage-engine
-s3-access-key=minioadmin
+s3-access-key=minio
 s3-secret-key=minioadmin
 s3-port=9000
 s3-use-http=ON

mysql-test/suite/s3/slave.cnf

@@ -16,7 +16,7 @@ s3-host-name="127.0.0.1"
 # Note: s3-host-name="localhost" doesn't work. It causes
 # libmarias3 to use the wrong variant of the protocol.
 s3-bucket=storage-engine
-s3-access-key=minioadmin
+s3-access-key=minio
 s3-secret-key=minioadmin
 s3-port=9000
 s3-use-http=ON