build: add paths-ignore for build-tarball workflow

In GitHub Actions, don't run build-tarball if the only changed files are
docs.

PR-URL: #40109
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: Michael Dawson <midawson@redhat.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

Author: Trott

.github/workflows/build-tarball.yml

@@ -3,12 +3,22 @@ name: Build from tarball
 on:
   pull_request:
     types: [opened, synchronize, reopened, ready_for_review]
+    paths-ignore:
+      - '.mailmap'
+      - '**.md'
+      - 'AUTHORS'
+      - 'doc/**'
   push:
     branches:
       - master
       - main
       - v[0-9]+.x-staging
       - v[0-9]+.x
+    paths-ignore:
+      - '.mailmap'
+      - '**.md'
+      - 'AUTHORS'
+      - 'doc/**'
 
 env:
   FLAKY_TESTS: dontcare