build: GitHub Action allows changelog path to be overridden.

action.yml

@@ -1,11 +1,19 @@
 name: Extract Changelog entries for most recent version
 description: Extracts entries from the changelog file for the most recent version and writes them to a file.
 inputs:
+  changelog-file:
+    description: 'Path to the changelog file, relative to the workspace.'
+    required: false
+    default: 'CHANGELOG.md'
   output-file:
     description: 'The file to write the extracted entries to, relative to the workspace.'
     required: true
 runs:
   using: 'docker'
   image: 'Dockerfile'
-  working-directory: /github/workspace
-  args: [ "changelog", "extract", "--quiet", "--output-file", "/github/workspace/${{ inputs.output-file }}" ]
+  args: [
+    "changelog", "extract",
+    "--quiet",
+    "--changelog", "/github/workspace/${{ inputs.changelog-file }}",
+    "--output-file", "/github/workspace/${{ inputs.output-file }}"
+  ]