[BUG] NVTX ranges not being closed in Frame._get_columns_by_label?

**Describe the bug**
When running the following Python script, it seems that the NVTX ranges aren't being closed. See screenshot below.

```python
import cudf
from cudf.testing._utils import assert_eq

if __name__ == "__main__":
for i in range(3):
gdf = cudf.DataFrame({"a": range(10)})
pdf = gdf.to_pandas()
assert_eq(gdf, pdf)
```

Then execute `nsys profile python nvtx_bug.py`.


I didn't see this problem with `cudf.Series`, only `cudf.DataFrame`.