ci: don't build for doc-only changes

Commit 0c55e10 introduced a
non-optional build step, but it is not needed when doing doc-only
changes.

Fixes: 0c55e10

Signed-off-by: Pablo Barbáchano <[email protected]>

Author: pb8o

.buildkite/pipeline_pr.py

@@ -14,6 +14,10 @@
     "agents": {"ag": 1},
 }
 
+changed_files = get_changed_files()
+DOC_ONLY_CHANGE = False
+if changed_files and all(f.suffix == ".md" for f in changed_files):
+    DOC_ONLY_CHANGE = True
 pipeline = BKPipeline(
     priority=DEFAULT_PRIORITY,
     timeout_in_minutes=45,
@@ -23,10 +27,9 @@
             "label": "🪶 Style",
         },
     ],
+    with_build_step=not DOC_ONLY_CHANGE,
 )
 
-changed_files = get_changed_files()
-
 # run sanity build of devtool if Dockerfile is changed
 if any(x.parent.name == "devctr" for x in changed_files):
     pipeline.build_group_per_arch(