upgrade: update dependency melos to v6 (#512)

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This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| [melos](https://melos.invertase.dev/~melos-latest)
([source](https://togithub.com/invertase/melos/tree/HEAD/packages/melos))
| dev_dependencies | major | `^5.0.0` -> `^6.0.0` |

---

### Release Notes

<details>
<summary>invertase/melos (melos)</summary>

###
[`v6.0.0`](https://togithub.com/invertase/melos/blob/HEAD/packages/melos/CHANGELOG.md#600)

[Compare
Source](https://togithub.com/invertase/melos/compare/melos-v5.3.0...melos-v6.0.0)

> Note: This release has breaking changes.

- **FIX**: Only enforce lockfile when it exists
([#&#8203;704](https://togithub.com/invertase/melos/issues/704)).
([be94adac](https://togithub.com/invertase/melos/commit/be94adacac71d8263079641229640932b387891a))
- **FEAT**: option to provide dependencies related filters from yaml
([#&#8203;698](https://togithub.com/invertase/melos/issues/698)).
([92be9858](https://togithub.com/invertase/melos/commit/92be9858cd64f35cce2d3a3ba2f4184cd32d0955))
- **FEAT**: add `--line-length` option to `melos format` command
([#&#8203;689](https://togithub.com/invertase/melos/issues/689)).
([048ab301](https://togithub.com/invertase/melos/commit/048ab301ca0f01f99d198c3ba6ca0f3c951078cf))
- **DOCS**: fix misalignment in readme
([#&#8203;699](https://togithub.com/invertase/melos/issues/699)).
([5e588ef9](https://togithub.com/invertase/melos/commit/5e588ef92d5e5ad25bb99be5a279305c4c07e9a9))
- **BREAKING** **FIX**: Make `melos analyze` always use `dart analyze`
([#&#8203;695](https://togithub.com/invertase/melos/issues/695)).
([2b16e360](https://togithub.com/invertase/melos/commit/2b16e3609bf3e00d15c42968dfbaeac2663a48c9))

</details>

---

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pubspec.yaml

@@ -5,4 +5,4 @@ environment:
 
 dev_dependencies:
   lints: any # Ignoring the version to allow editing across SDK versions.
-  melos: ^5.0.0
+  melos: ^6.0.0