Remove decreasing of created connections count when releasing not owned by connection pool connection(fixes issue #2832).

[petyaslavova]

Pull Request check-list

Please make sure to review and check all of these items:

• Do tests and lints pass with this change?
• Do the CI tests pass with this change (enable it first in your forked repo and wait for the github action build to finish)?
• Is the new or changed code fully tested?
• Is a documentation update included (if this change modifies existing APIs, or introduces new ones)?
• Is there an example added to the examples folder (if applicable)?
• Was the change added to CHANGES file?

NOTE: these things are not required to open a PR and can be done
afterwards / while the PR is open.

Description of change

• Removing decreasing of created connections count when releasing not owned by connection pool connection(issue #2832).
• Fixed another issue that was allowing adding connections to a pool owned by other pools.
• Adding unit tests.