Update pluggy requirement from >=0.3.1 to >=1.6.0

Updates the requirements on [pluggy](https://github.com/pytest-dev/pluggy) to permit the latest version.
- [Changelog](https://github.com/pytest-dev/pluggy/blob/main/CHANGELOG.rst)
- [Commits](pytest-dev/pluggy@0.3.1...1.6.0)

---
updated-dependencies:
- dependency-name: pluggy
  dependency-version: 1.6.0
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

test-requirements.txt

@@ -2,7 +2,7 @@ coverage>=4.0.3
 nose>=1.3.7
 pytest
 pytest-cov
-pluggy>=0.3.1
+pluggy>=1.6.0
 randomize>=0.13
 sphinx>=1.4 # BSD
 sphinx_markdown_tables