fix: runner startup silent failure (#914)

Closes #909

### Summary of Changes

- failing to start runner process now logs an appropriate message
informs the user via popup again
- command is now successfully passed to the runner component, if changed

---------

Co-authored-by: megalinter-bot <129584137+megalinter-bot@users.noreply.github.com>

packages/safe-ds-lang/src/language/runner/safe-ds-runner.ts

@@ -104,8 +104,10 @@ export class SafeDsRunner {
                 this.logging.outputInfo(`Using safe-ds-runner version: ${versionString}`);
             }
         } catch (error) {
-            this.logging.outputError(`Could not start runner: ${error}`);
-            this.logging.displayError('The runner process could not be started.');
+            this.logging.outputError(`Could not start runner: ${error instanceof Error ? error.message : error}`);
+            this.logging.displayError(
+                `The runner process could not be started: ${error instanceof Error ? error.message : error}`,
+            );
             return;
         }
         // Start the runner at the specified port
@@ -414,6 +416,9 @@ export class SafeDsRunner {
             process.on('close', (code) => {
                 reject(new Error(`The subprocess shut down: ${code}`));
             });
+            process.on('error', (err) => {
+                reject(new Error(`The subprocess could not be started (${err.message})`));
+            });
         });
     }
 

packages/safe-ds-vscode/src/extension/mainClient.ts

@@ -382,6 +382,9 @@ const registerVSCodeWatchers = function () {
         if (event.affectsConfiguration('safe-ds.runner.command')) {
             // Try starting runner
             logOutput('Safe-DS Runner Command was updated');
+            services.runtime.Runner.updateRunnerCommand(
+                vscode.workspace.getConfiguration('safe-ds.runner').get<string>('command')!,
+            );
             if (!services.runtime.Runner.isPythonServerAvailable()) {
                 services.runtime.Runner.startPythonServer();
             } else {