Bump pyyaml from 3.12 to 5.1 in /tests/milvus_benchmark

Bumps [pyyaml](https://github.com/yaml/pyyaml) from 3.12 to 5.1.
- [Release notes](https://github.com/yaml/pyyaml/releases)
- [Changelog](https://github.com/yaml/pyyaml/blob/master/CHANGES)
- [Commits](https://github.com/yaml/pyyaml/compare/3.12...5.1)
Signed-off-by: Ndependabot[bot] <support@github.com>
Former-commit-id: 24d3855981565733ad377ba669262fe587444eb4

tests/milvus_benchmark/requirements.txt

 numpy==1.16.3
 pymilvus>=0.1.18
-pyyaml==3.12
+pyyaml==5.1
 docker==4.0.2
 tableprint==0.8.0
 ansicolors==1.1.8
\ No newline at end of file