currency/manager: remove deadlock potential in concurrent operations

[shazbert]

PR Description

Resolves intermittent deadlock observed in CI builds. Example

Type of change

Please delete options that are not relevant and add an x in [] as item is complete.

• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] This change requires a documentation update

How has this been tested

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration and also consider improving test coverage whilst working on a certain feature or package.

• [ ] go test ./... -race
• [ ] golangci-lint run
• [ ] Test X

Checklist

• [ ] My code follows the style guidelines of this project
• [ ] I have performed a self-review of my own code
• [ ] I have commented my code, particularly in hard-to-understand areas
• [ ] I have made corresponding changes to the documentation and regenerated documentation via the documentation tool
• [ ] My changes generate no new warnings
• [ ] I have added tests that prove my fix is effective or that my feature works
• [ ] New and existing unit tests pass locally and on Github Actions with my changes
• [ ] Any dependent changes have been merged and published in downstream modules

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 37.77%. Comparing base (34ef09d) to head (4803a9c). Report is 1 commits behind head on master.

Additional details and impacted files

[](https://app.codecov.io/gh/thrasher-corp/gocryptotrader/pull/1545?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=thrasher-corp) ```diff @@ Coverage Diff @@ ## master #1545 +/- ## ========================================== + Coverage 35.89% 37.77% +1.87% ========================================== Files 409 409 Lines 177453 147697 -29756 ========================================== - Hits 63699 55789 -7910 + Misses 105899 84044 -21855 - Partials 7855 7864 +9 ``` | [Files](https://app.codecov.io/gh/thrasher-corp/gocryptotrader/pull/1545?dropdown=coverage&src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=thrasher-corp) | Coverage Δ | | |---|---|---| | [currency/manager.go](https://app.codecov.io/gh/thrasher-corp/gocryptotrader/pull/1545?src=pr&el=tree&filepath=currency%2Fmanager.go&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=thrasher-corp#diff-Y3VycmVuY3kvbWFuYWdlci5nbw==) | `94.96% <100.00%> (+1.53%)` | :arrow_up: | ... and [386 files with indirect coverage changes](https://app.codecov.io/gh/thrasher-corp/gocryptotrader/pull/1545/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=thrasher-corp)