Update labels in GitHub files (#494)

- Make labels empty in the issue templates
  - Our maintainer guides tells not to add labels until triage.
    (See https://stylelint.io/maintainer-guide/issues#labels)
- Replace labels for Dependabot pull requests

.github/ISSUE_TEMPLATE/bug.yml

@@ -1,7 +1,7 @@
 name: "\U0001F41B Bug Report"
 description: File a bug report
 title: '[Bug]: '
-labels: ['Bug']
+labels: []
 body:
   - type: markdown
     attributes:

.github/ISSUE_TEMPLATE/docs.yml

@@ -1,7 +1,7 @@
 name: "\U0001F4DD Documentation Issue"
 description: Report an issue with the documentation.
 title: '[Docs]: '
-labels: ['Docs']
+labels: []
 body:
   - type: markdown
     attributes:

.github/ISSUE_TEMPLATE/feature.yml

@@ -1,7 +1,7 @@
 name: "\U0001F680 Feature Request"
 description: Suggest a new feature for the project
 title: '[Feature]: '
-labels: ['Suggestion']
+labels: []
 body:
   - type: markdown
     attributes:

.github/dependabot.yml

@@ -7,8 +7,7 @@ updates:
     open-pull-requests-limit: 5
     versioning-strategy: increase
     labels:
-      - 'Dependencies'
-      - 'For Uncommitted Issue'
+      - 'pr: dependencies'
     ignore:
       - dependency-name: p-wait-for
         update-types: [version-update:semver-major]
@@ -19,5 +18,4 @@ updates:
     schedule:
       interval: monthly
     labels:
-      - 'Dependencies'
-      - 'For Uncommitted Issue'
+      - 'pr: dependencies'