Update test

Update the test that checks that the existing edit_uri value in a
mkdocs.yml won't be overridden by `patchMkdocsYmlPreBuild` so that it
checks the value of 'edit_uri' was not updated rather than just checking
for the existence of the substring. This change is needed because the
substring will exist in the file but as the `repo_url` value which is
expected after the changes in the previous commits.

Signed-off-by: Isabel Tomb <isabelgtomb@gmail.com>

plugins/techdocs-node/src/stages/generate/helpers.test.ts

@@ -295,7 +295,7 @@ describe('helpers', () => {
         'edit_uri: https://github.com/backstage/backstage/edit/main/docs',
       );
       expect(updatedMkdocsYml.toString()).not.toContain(
-        'https://github.com/neworg/newrepo',
+        'edit_uri: https://github.com/neworg/newrepo',
       );
     });