Force CI schema URL to be absolute

In order for workers loaded from `data://` as the
ones loaded by monaco, we use absolute URLs to fetch
schema files, hence the `location.origin` reference.
This prevents error: "Failed to execute 'fetch' on 'WorkerGlobalScope'"

app/assets/javascripts/editor/extensions/editor_ci_schema_ext.js

@@ -24,8 +24,16 @@ export class CiSchemaExtension extends EditorLiteExtension {
       .replace(':filename', EXTENSION_CI_SCHEMA_FILE_NAME_MATCH);
     const modelFileName = this.getModel().uri.path.split('/').pop();
 
+    // In order for workers loaded from `data://` as the
+    // ones loaded by monaco, we use absolute URLs to fetch
+    // schema files, hence the `location.origin` reference.
+    // This prevents error:
+    //   "Failed to execute 'fetch' on 'WorkerGlobalScope'"
+    // eslint-disable-next-line no-restricted-globals
+    const absoluteSchemaUrl = location.origin + ciSchemaUri;
+
     registerSchema({
-      uri: ciSchemaUri,
+      uri: absoluteSchemaUrl,
       fileMatch: [modelFileName],
     });
   }

spec/frontend/editor/editor_ci_schema_ext_spec.js

 import { languages } from 'monaco-editor';
+import { TEST_HOST } from 'helpers/test_constants';
 import EditorLite from '~/editor/editor_lite';
 import { CiSchemaExtension } from '~/editor/extensions/editor_ci_schema_ext';
 import { EXTENSION_CI_SCHEMA_FILE_NAME_MATCH } from '~/editor/constants';
@@ -73,7 +74,7 @@ describe('~/editor/editor_ci_config_ext', () => {
         });
 
         expect(getConfiguredYmlSchema()).toEqual({
-          uri: `/${mockProjectNamespace}/${mockProjectPath}/-/schema/${mockRef}/${EXTENSION_CI_SCHEMA_FILE_NAME_MATCH}`,
+          uri: `${TEST_HOST}/${mockProjectNamespace}/${mockProjectPath}/-/schema/${mockRef}/${EXTENSION_CI_SCHEMA_FILE_NAME_MATCH}`,
           fileMatch: [defaultBlobPath],
         });
       });
@@ -87,7 +88,7 @@ describe('~/editor/editor_ci_config_ext', () => {
         });
 
         expect(getConfiguredYmlSchema()).toEqual({
-          uri: `/${mockProjectNamespace}/${mockProjectPath}/-/schema/master/${EXTENSION_CI_SCHEMA_FILE_NAME_MATCH}`,
+          uri: `${TEST_HOST}/${mockProjectNamespace}/${mockProjectPath}/-/schema/master/${EXTENSION_CI_SCHEMA_FILE_NAME_MATCH}`,
           fileMatch: ['another-ci-filename.yml'],
         });
       });