fix(aci): fix error state for nonexistent monitor details (#102929)

`!project` check was causing an infinite loading spinner on the monitor
details page for nonexistent monitors

also improved the error message for automation details page when the
resource does not exist

Author: ameliahsu

static/app/views/automations/detail.tsx

@@ -175,6 +175,7 @@ function AutomationDetailLoadingStates({automationId}: {automationId: string}) {
     data: automation,
     isPending,
     isError,
+    error,
     refetch,
   } = useAutomationQuery(automationId);
 
@@ -183,7 +184,12 @@ function AutomationDetailLoadingStates({automationId}: {automationId: string}) {
   }
 
   if (isError) {
-    return <LoadingError onRetry={refetch} />;
+    return (
+      <LoadingError
+        message={error.status === 404 ? t('The alert could not be found.') : undefined}
+        onRetry={refetch}
+      />
+    );
   }
 
   return <AutomationDetailContent automation={automation} />;

static/app/views/detectors/detail.tsx

@@ -14,8 +14,10 @@ import {useDetectorQuery} from 'sentry/views/detectors/hooks';
 function DetectorDetailsLoadingStates({
   detectorId,
   project,
+  isFetchingProjects,
 }: {
   detectorId: string;
+  isFetchingProjects: boolean;
   project: Project | undefined;
 }) {
   const {
@@ -26,7 +28,7 @@ function DetectorDetailsLoadingStates({
     refetch,
   } = useDetectorQuery(detectorId);
 
-  if (isPending || !project) {
+  if (isPending || isFetchingProjects) {
     return <LoadingIndicator />;
   }
 
@@ -67,7 +69,11 @@ export default function DetectorDetails() {
       id="DetectorDetails-Body"
       isLoading={isLoading}
     >
-      <DetectorDetailsLoadingStates detectorId={params.detectorId} project={project} />
+      <DetectorDetailsLoadingStates
+        detectorId={params.detectorId}
+        project={project}
+        isFetchingProjects={isFetchingProjects}
+      />
     </VisuallyCompleteWithData>
   );
 }