CI: Minor improvements to Markdown action (#14979)

Author: eksperimental

.github/workflows/ci-markdown.yml renamed to .github/workflows/markdown.yml

@@ -1,38 +1,37 @@
 # SPDX-License-Identifier: Apache-2.0
 # SPDX-FileCopyrightText: 2021 The Elixir Team
 
-name: CI for Markdown content
+name: Markdown Content
 
 on:
   push:
     branches:
       - "main"
 
-    paths:
+    paths: &paths-filter
       - "**/*.md"
-      - ".github/workflows/ci-markdown.yml"
-      - ".markdownlint-cli2.jsonc"
+      - .github/workflows/markdown.yml
+      - .markdownlint-cli2.jsonc
 
   pull_request:
-    paths:
-      - "**/*.md"
-      - ".github/workflows/ci-markdown.yml"
-      - ".markdownlint-cli2.jsonc"
+    paths: *paths-filter
 
   workflow_dispatch:
 
 permissions:
   contents: read
 
+env:
+  LANG: C.UTF-8
+
 jobs:
   lint:
     name: Lint Markdown content
+    runs-on: ubuntu-latest
 
     strategy:
       fail-fast: false
 
-    runs-on: ubuntu-latest
-
     steps:
       - uses: actions/checkout@1af3b93b6815bc44a9784bd300feb67ff0d1eeb3 # v6.0.0