Update psutil requirement from <6,>=5 to >=6.0.0,<7 (#1522)

Updates the requirements on [psutil](https://github.com/giampaolo/psutil) to permit the latest version.
- [Changelog](https://github.com/giampaolo/psutil/blob/master/HISTORY.rst)
- [Commits](giampaolo/psutil@release-5.0.0...release-6.0.0)

---
updated-dependencies:
- dependency-name: psutil
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

requirements/testing.txt

@@ -11,7 +11,7 @@ flake8>=5.0.4,<8
 black>=22.8.0; python_version=="3.6"
 black==22.10.0; python_version>"3.6"
 click==8.0.4  # black is affected by https://github.com/pallets/click/issues/2225
-psutil>=5,<6
+psutil>=6.0.0,<7
 #  used only under slack_sdk/*_store
 boto3<=2
 # For AWS tests