chore(build): fix flaky validate examples step (#11705)

**What this PR does / why we need it**:
`validate-example-configs` step is flaky and fails with the following
error: `[Text file busy](bash: line 1: ./cmd/loki/loki: Text file busy)`

looks like the recently added `validate-dev-cluster-config` runs in
parallel. since both steps run loki target first, they often end up
updating the binary when the other step is executing it.

this pr fixes this by running these steps sequentially

**Which issue(s) this PR fixes**:
Fixes #<issue number>

**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`
- [ ] 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](d10549e)
- [ ] 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](0d4416a)

.drone/drone.jsonnet

@@ -640,7 +640,7 @@ local build_image_tag = '0.33.0';
         'GIT_TARGET_BRANCH="$DRONE_TARGET_BRANCH"',
       ]) { depends_on: ['loki'], when: onPRs },
       make('validate-example-configs', container=false) { depends_on: ['loki'] },
-      make('validate-dev-cluster-config', container=false) { depends_on: ['loki'] },
+      make('validate-dev-cluster-config', container=false) { depends_on: ['validate-example-configs'] },
       make('check-example-config-doc', container=false) { depends_on: ['clone'] },
       {
         name: 'build-docs-website',

.drone/drone.yml

@@ -306,7 +306,7 @@ steps:
 - commands:
   - make BUILD_IN_CONTAINER=false validate-dev-cluster-config
   depends_on:
-  - loki
+  - validate-example-configs
   environment: {}
   image: grafana/loki-build-image:0.33.0
   name: validate-dev-cluster-config
@@ -2113,6 +2113,6 @@ kind: secret
 name: gpg_private_key
 ---
 kind: signature
-hmac: fe7669a21410ae5f2d1ad6b6205fdc582af874f65f7bd6a679731a88174e3a1c
+hmac: 457592d17208477ceb480f81dbdb88f7b95a5ad015c88d9d6fed06c2422a52f9
 
 ...