Merge branch 'lint-for-changelog' into 'master'

Add linting for duplicate CHANGELOG entries

## What does this MR do?

Extend `scripts/lint-doc.sh` so that it checks that there are no duplicate versions in CHANGELOG.

See merge request !6039

CHANGELOG

@@ -603,6 +603,7 @@ v 8.10.0
   - Export and import avatar as part of project import/export
   - Fix migration corrupting import data for old version upgrades
   - Show tooltip on GitLab export link in new project page
+  - Fix import_data wrongly saved as a result of an invalid import_url !5206
 
 v 8.9.9
   - Exclude some pending or inactivated rows in Member scopes
@@ -623,12 +624,6 @@ v 8.9.6
   - Keeps issue number when importing from Gitlab.com
   - Add Pending tab for Builds (Katarzyna Kobierska, Urszula Budziszewska)
 
-v 8.9.7 (unreleased)
-  - Fix import_data wrongly saved as a result of an invalid import_url
-
-v 8.9.6
-  - Fix importing of events under notes for GitLab projects
-
 v 8.9.5
   - Add more debug info to import/export and memory killer. !5108
   - Fixed avatar alignment in new MR view. !5095
@@ -1894,7 +1889,7 @@ v 8.1.3
   - Use issue editor as cross reference comment author when issue is edited with a new mention
   - Add Facebook authentication
 
-v 8.1.1
+v 8.1.2
   - Fix cloning Wiki repositories via HTTP (Stan Hu)
   - Add migration to remove satellites directory
   - Fix specific runners visibility

scripts/lint-doc.sh

@@ -10,6 +10,15 @@ then
   exit 1
 fi
 
+# Ensure that the CHANGELOG does not contain duplicate versions
+DUPLICATE_CHANGELOG_VERSIONS=$(grep --extended-regexp '^v [0-9.]+' CHANGELOG | sed 's| (unreleased)||' | sort | uniq -d)
+if [ "${DUPLICATE_CHANGELOG_VERSIONS}" != "" ]
+then
+  echo '✖ ERROR: Duplicate versions in CHANGELOG:' >&2
+  echo "${DUPLICATE_CHANGELOG_VERSIONS}" >&2
+  exit 1
+fi
+
 echo "✔ Linting passed"
 exit 0