Fix EditorConfig lint errors

## EditorConfig Linting Failures

Linting failures were detected in the automated EditorConfig lint workflow run.

### Workflow Details

- Run: https://github.com/stdlib-js/stdlib/actions/runs/26006953643
- Type: EditorConfig Linting
- Date: 2026-05-18 00:21:37 UTC

### Error Details

```
Linting files for basic formatting errors...
Downloading v3.6.1
lib/node_modules/@stdlib/ndarray/base/slice-assign/examples/index.js:
78-94: Wrong indentation type(spaces instead of tabs)

1 errors found
make: *** [/home/runner/work/stdlib/stdlib/tools/make/lib/lint/editorconfig.mk:90: lint-editorconfig-files] Error 1
```

### Pull Request Instructions

- Please use the following PR title format:
"chore: fix EditorConfig lint errors (issue #)".
- Reference this issue in the "Related Issues" section of the PR body as "resolves #".

Start with lib/node_modules/@stdlib/ndarray/base/slice-assign/examples/index.js and inspect lines 78-94, where the EditorConfig workflow reports spaces instead of tabs. Run the EditorConfig lint workflow or the lint-editorconfig-files target in tools/make/lib/lint/editorconfig.mk. Done means the lint reports no formatting errors.

索引モデルが issue の本文から書いたものです。