Restore original lint backend drone step (#1904)

Drone builds are broken because the lint step was [changed to run all
lint
tasks](https://github.com/grafana/oncall/pull/1849/files#diff-b54b39f1afced2465e1f3641db9d5bbf4f3a7fcf890996dfedd3c197bcb7f8c7)
and the plugin is not there when running frontend lint commands. Restore
the original step to unblock drone.

.drone.yml

@@ -61,13 +61,15 @@ steps:
       ref:
         - refs/tags/v*.*.*
 
-  - name: Lint Everything
+  - name: Lint Backend
     image: python:3.11.3
     environment:
       DJANGO_SETTINGS_MODULE: settings.ci-test
     commands:
       - pip install $(grep "pre-commit" engine/requirements.txt)
-      - pre-commit run --all-files
+      - pre-commit run isort --all-files
+      - pre-commit run black --all-files
+      - pre-commit run flake8 --all-files
 
   - name: Unit Test Backend
     image: python:3.11.3
@@ -112,7 +114,7 @@ steps:
       config:
         from_secret: gcr_admin
     depends_on:
-      - Lint Everything
+      - Lint Backend
       - Unit Test Backend
       - Image Tag
 
@@ -132,7 +134,7 @@ steps:
       username:
         from_secret: docker_username
     depends_on:
-      - Lint Everything
+      - Lint Backend
       - Unit Test Backend
       - Image Tag
     when:
@@ -416,6 +418,6 @@ kind: secret
 name: drone_token
 ---
 kind: signature
-hmac: 9eb4e539c2313ae319d12d1f5149ddf93ea017720b1690abe5e1730e2a1489f2
+hmac: a428b546ec4557971dfe3c7eeeac70ddf08faea7336607647ad3f146dd4cb46a
 
 ...