ci: Verific skipping conditional on github.ref

Docs jobs should not skip on concurrent jobs (in case a non-docs job is already running, such as when a commit has been tagged for docs-preview).
However, a successful `test-verific` can allow for a future docs job to skip testing and go straight to the preview.

.github/workflows/test-verific.yml

@@ -1,6 +1,10 @@
 name: Build and run tests with Verific (Linux)
 
 on: [push, pull_request]
+# docs builds are needed for anything on main, any tagged versions, and any tag
+# or branch starting with docs-preview
+env:
+  is_docs_job: ${{ github.ref == 'refs/heads/main' || startsWith(github.ref, 'refs/heads/docs-preview') || startsWith(github.ref, 'refs/tags/') }}
 
 jobs:
   pre-job:
@@ -15,9 +19,10 @@ jobs:
           # don't cancel previous builds
           cancel_others: 'false'
           # only run on push *or* pull_request, not both
-          concurrent_skipping: 'same_content_newer'
-          # we have special actions when running on main, so this should be off
-          skip_after_successful_duplicate: 'false'
+          # unless this is a build which needs to run for docs generation
+          concurrent_skipping: ${{ env.is_docs_job && 'never' || 'same_content_newer' }}
+          # we can skip testing if it has already passed
+          skip_after_successful_duplicate: 'true'
 
   test-verific:
     needs: pre-job
@@ -74,7 +79,7 @@ jobs:
   prepare-docs:
     name: Generate docs artifact
     needs: [pre-job, test-verific]
-    if: needs.pre-job.outputs.should_skip != 'true'
+    if: needs.pre-job.outputs.should_skip != 'true' || env.is_docs_job
     runs-on: [self-hosted, linux, x64, fast]
     steps:
       - name: Checkout Yosys
@@ -112,7 +117,7 @@ jobs:
             docs/source/code_examples
 
       - name: Trigger RTDs build
-        if: ${{ github.ref == 'refs/heads/main' || startsWith(github.ref, 'refs/heads/docs-preview') || startsWith(github.ref, 'refs/tags/') }}
+        if: ${{ env.is_docs_job }}
         uses: dfm/[email protected]
         with:
           webhook_url: ${{ secrets.RTDS_WEBHOOK_URL }}