ci: use 'concurrency' feature in fuzzing.yml

It looks like we just missed the fuzzing.yml workflow when worked on
adding this feature to our CI process in tarantool#6446.

Follows up tarantool/tarantool-qa#100

NO_DOC=ci
NO_CHANGELOG=ci
NO_TEST=ci

.github/workflows/fuzzing.yml

@@ -15,6 +15,26 @@ on:
   pull_request:
     types: [opened, reopened, synchronize, labeled]
 
+concurrency:
+  # Update of a developer branch cancels the previously scheduled workflow
+  # run for this branch. However, the 'master' branch, release branch (1.10,
+  # 2.8, etc.), and tag workflow runs are never canceled.
+  #
+  # We use a trick here: define the concurrency group as 'workflow run ID' +
+  # 'workflow run attempt' because it is a unique combination for any run.
+  # So it effectively discards grouping.
+  #
+  # Important: we cannot use `github.sha` as a unique identifier because
+  # pushing a tag may cancel a run that works on a branch push event.
+  group: ${{ (
+    github.ref == 'refs/heads/master' ||
+    github.ref == 'refs/heads/1.10' ||
+    startsWith(github.ref, 'refs/heads/2.') ||
+    startsWith(github.ref, 'refs/tags/')) &&
+    format('{0}-{1}', github.run_id, github.run_attempt) ||
+    format('{0}-{1}', github.workflow, github.ref) }}
+  cancel-in-progress: true
+
 jobs:
   fuzzing:
     # Run on push to the 'master' and release branches of tarantool/tarantool