CHANGED - add concurrency to high volume workflows (MetaMask#5709)

## **Description**

By default, GitHub Actions allows multiple jobs within the same
workflow, multiple workflow runs within the same repository, and
multiple workflow runs across a repository owner's account to run
concurrently. This means that multiple instances of the same workflow or
job can run at the same time, performing the same steps.

https://docs.github.com/en/actions/writing-workflows/choosing-what-your-workflow-does/control-the-concurrency-of-workflows-and-jobs

GitHub Actions also allows you to disable concurrent execution. This can
be useful for controlling your account’s or organization’s resources in
situations where running multiple workflows or jobs at the same time
could cause conflicts or consume more Actions minutes and storage than
expected.

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## **Related issues**

Fixes/Reduces: pending workflows

Author: waskow-consensys

.github/workflows/main.yml

@@ -5,6 +5,10 @@ on:
     branches: [main]
   pull_request:
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
 jobs:
   check-workflows:
     name: Check workflows