`@stdlib/complex/float32/base/assert/is-equal` missing benchmark configuration in `manifest.json`

### Description

When building or running `C` benchmarks for complex BLAS level-2 routines (specifically [`cgemv`](https://github.com/stdlib-js/stdlib/pull/11739)), the compilation fails

### Related Issues

_No response_

### Questions

No.

### Demo

_No response_

### Reproduction

```shell
1. Identify any package which depends on `@stdlib/complex/float32/base/assert/is-equal`.
2. Run a benchmark build.
3. Observe compilation failure due to missing `is_equal.h`.
```

### Expected Results

The benchmark should compile successfully.

### Actual Results

### Version

_No response_

### Environments

N/A

### Browser Version

_No response_

### Node.js / npm Version

_No response_

### Platform

_No response_

### Checklist

- [x] Read and understood the [Code of Conduct](https://github.com/stdlib-js/stdlib/blob/develop/CODE_OF_CONDUCT.md).
- [x] Searched for existing issues and pull requests.