ci(deploy): add a pages concurrency group

There can only be one deployment at any one time and it has to be a full
snapshot. No piecemeal updates. Might as well use a concurrency limit to
kill any other jobs that get in our way. Not that there ever should be
any, considering the way this job is launched currently.

Signed-off-by: Randolph Sapp <rs@ti.com>

Author: StaticRocket

.github/workflows/deploy.yml

@@ -8,6 +8,10 @@ on:  # yamllint disable-line rule:truthy
     types:
       - completed
 
+concurrency:
+  group: pages
+  cancel-in-progress: true
+
 permissions:
   contents: read