Fix merging partition config into existing launchpad config (#17688)

## Summary & Motivation
Fixes #17522

## How I Tested These Changes

created a job in the toys repository to test this

js_modules/dagster-ui/packages/ui-core/src/launchpad/LaunchpadSession.tsx

@@ -519,8 +519,8 @@ const LaunchpadSession: React.FC<LaunchpadSessionProps> = (props) => {
       } else {
         runConfigYaml = yaml.stringify(
           merge(
-            yaml.parse(sanitizeConfigYamlString(partition.runConfigOrError.yaml)),
             yaml.parse(sanitizeConfigYamlString(currentSession.runConfigYaml)),
+            yaml.parse(sanitizeConfigYamlString(partition.runConfigOrError.yaml)),
           ),
         );
       }

python_modules/dagster-test/dagster_test/toys/partition_config.py

@@ -0,0 +1,16 @@
+from dagster import job, op, static_partitioned_config
+
+
+@static_partitioned_config(["a", "b", "c"])
+def partconf(partition):
+    return {"ops": {"op1": {"letter": partition}}}
+
+
+@op(config_schema={"letter": str})
+def op1():
+    ...
+
+
+@job(config=partconf)
+def job_with_partition_config():
+    op1()

python_modules/dagster-test/dagster_test/toys/repo.py

@@ -6,7 +6,14 @@
 warnings.filterwarnings("ignore", category=ExperimentalWarning)
 
 import pendulum
-from dagster import AssetMaterialization, Output, graph, load_assets_from_modules, op, repository
+from dagster import (
+    AssetMaterialization,
+    Output,
+    graph,
+    load_assets_from_modules,
+    op,
+    repository,
+)
 
 from dagster_test.toys import big_honkin_asset_graph as big_honkin_asset_graph_module
 from dagster_test.toys.asset_sensors import get_asset_sensors_repo
@@ -18,7 +25,10 @@
     upstream_repo_assets,
 )
 from dagster_test.toys.dynamic import dynamic_job
-from dagster_test.toys.error_monster import error_monster_failing_job, error_monster_passing_job
+from dagster_test.toys.error_monster import (
+    error_monster_failing_job,
+    error_monster_passing_job,
+)
 from dagster_test.toys.graph_backed_assets import graph_backed_asset
 from dagster_test.toys.hammer import hammer_default_executor_job
 from dagster_test.toys.input_managers import df_stats_job
@@ -32,6 +42,7 @@
 from dagster_test.toys.multi_inputs_outputs import multi_inputs_outputs_job
 from dagster_test.toys.notebooks import hello_world_notebook_pipeline
 from dagster_test.toys.nothing_input import nothing_job
+from dagster_test.toys.partition_config import job_with_partition_config
 from dagster_test.toys.retries import retry_job
 from dagster_test.toys.run_status_sensors import (
     cross_repo_job_sensor,
@@ -57,8 +68,12 @@
     auto_materialize_large_static_graph as auto_materialize_large_static_graph,
     auto_materialize_large_time_graph as auto_materialize_large_time_graph,
 )
-from .auto_materializing.repo_1 import auto_materialize_repo_1 as auto_materialize_repo_1
-from .auto_materializing.repo_2 import auto_materialize_repo_2 as auto_materialize_repo_2
+from .auto_materializing.repo_1 import (
+    auto_materialize_repo_1 as auto_materialize_repo_1,
+)
+from .auto_materializing.repo_2 import (
+    auto_materialize_repo_2 as auto_materialize_repo_2,
+)
 from .schedules import get_toys_schedules
 from .sensors import get_toys_sensors
 
@@ -101,6 +116,7 @@ def toys_repository():
             unreliable_job,
             dynamic_job,
             model_job,
+            job_with_partition_config,
             multi_inputs_outputs_job,
             hello_world_notebook_pipeline,
             *software_defined_assets,