Fix job search when command_version is None

Fix 500 response when searching jobs via API as seen in BioBlend
tests on release_23.2 and dev, e.g.:

https://github.com/galaxyproject/bioblend/actions/runs/7090125691/job/19296402084#step:10:3256

Broken in galaxyproject#16778 .

lib/galaxy/schema/jobs.py

@@ -157,7 +157,7 @@ class EncodedDatasetJobInfo(EncodedDataItemSourceId):
 
 
 class EncodedJobDetails(JobSummary):
-    command_version: str = Field(
+    command_version: Optional[str] = Field(
         ...,
         title="Command Version",
         description="Tool version indicated during job execution.",