fix: say how to run the schema check step 0 skips

Without jsonschema the step printed only the missing module, and the run then read COMPLETE while PR validation runs the same check. The skip now names the install command and the PR check.

scripts/pipeline.py

@@ -721,7 +721,13 @@ def main() -> None:
     # `cores: [81]` unquoted passed the whole pipeline and failed CI on push.
     # jsonschema is tooling only, so its absence skips the step.
     if importlib.util.find_spec("jsonschema") is None:
-        skip_notice("validate_schemas", "jsonschema not installed")
+        # The skip names the install and what still runs the check, or a
+        # contributor read SKIPPED, then COMPLETE, and met the failure on push.
+        skip_notice(
+            "validate_schemas",
+            "jsonschema not installed. PR validation runs this check: "
+            'pip install "jsonschema[format-nongpl]"',
+        )
         results["validate_schemas"] = SKIPPED
     else:
         ok, _ = run(