linguist-backend: fix config value being required

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>

.changeset/new-sheep-cover.md

@@ -0,0 +1,5 @@
+---
+'@backstage/plugin-linguist-backend': patch
+---
+
+When creating the router using `createRouterFromConfig` or using the plugin for the new backend system the `linguist.useSourceLocation` configuration is now optional.

plugins/linguist-backend/src/service/router.ts

@@ -150,9 +150,8 @@ export async function createRouterFromConfig(routerOptions: RouterOptions) {
       );
     }
     pluginOptions.batchSize = config.getOptionalNumber('linguist.batchSize');
-    pluginOptions.useSourceLocation = config.getBoolean(
-      'linguist.useSourceLocation',
-    );
+    pluginOptions.useSourceLocation =
+      config.getOptionalBoolean('linguist.useSourceLocation') ?? false;
     pluginOptions.age = config.getOptionalConfig('linguist.age') as
       | HumanDuration
       | undefined;