Fixes missing braces in CopyLayer.__str__()

[codecov[bot]]

Codecov Report

Base: 52.22% // Head: 52.22% // No change to project coverage :thumbsup:

Coverage data is based on head (5f1669e) compared to base (6323d77). Patch coverage: 0.00% of modified lines in pull request are covered.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #518 +/- ## ======================================= Coverage 52.22% 52.22% ======================================= Files 124 124 Lines 8307 8307 Branches 1025 1025 ======================================= Hits 4338 4338 Misses 3792 3792 Partials 177 177 ``` | [Impacted Files](https://codecov.io/gh/PolyJIT/benchbuild/pull/518?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=PolyJIT) | Coverage Δ | | |---|---|---| | [benchbuild/environments/domain/model.py](https://codecov.io/gh/PolyJIT/benchbuild/pull/518/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=PolyJIT#diff-YmVuY2hidWlsZC9lbnZpcm9ubWVudHMvZG9tYWluL21vZGVsLnB5) | `89.74% <0.00%> (ø)` | | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=PolyJIT). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=PolyJIT)

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