**What this PR does / why we need it**:
It bumps the version for the MinIO Helm Chart to v4.0.15. 
The current MinIO version (4.0.12) has a bug where it throws warnings
for incorrect types.

```
coalesce.go:237: warning: skipped value for loki.minio.additionalLabels: Not a table.
coalesce.go:237: warning: skipped value for loki.minio.additionalAnnotations: Not a table.
``` 

**Which issue(s) this PR fixes**:
None

**Special notes for your reviewer**:

**Checklist**
- [X] Reviewed the
[`CONTRIBUTING.md`](https://github.com/grafana/loki/blob/main/CONTRIBUTING.md)
guide (**required**)
- [ ] Documentation added
- [ ] Tests updated
- [ ] `CHANGELOG.md` updated
- [ ] If the change is worth mentioning in the release notes, add
`add-to-release-notes` label
- [ ] Changes that require user attention or interaction to upgrade are
documented in `docs/sources/setup/upgrade/_index.md`
- [X] For Helm chart changes bump the Helm chart version in
`production/helm/loki/Chart.yaml` and update
`production/helm/loki/CHANGELOG.md` and
`production/helm/loki/README.md`. [Example
PR](https://github.com/grafana/loki/commit/d10549e3ece02120974929894ee333d07755d213)
- [ ] If the change is deprecating or removing a configuration option,
update the `deprecated-config.yaml` and `deleted-config.yaml` files
respectively in the `tools/deprecated-config-checker` directory.
[Example
PR](https://github.com/grafana/loki/pull/10840/commits/0d4416a4b03739583349934b96f272fb4f685d15)

---------

Co-authored-by: Michel Hollands <42814411+MichelHollands@users.noreply.github.com>