feat(config): add applyMigrations function

lib/config/migration.ts

@@ -4,8 +4,7 @@ import { dequal } from 'dequal';
 import { logger } from '../logger';
 import { clone } from '../util/clone';
 import { getGlobalConfig } from './global';
-import type { Migration } from './migrations/migration';
-import { RequiredStatusChecksMigration } from './migrations/required-status-checks-migration';
+import { applyMigrations } from './migrations';
 import { getOptions } from './options';
 import { removedPresets } from './presets/common';
 import type {
@@ -59,12 +58,7 @@ export function migrateConfig(
       'peerDependencies',
     ];
     const { migratePresets } = getGlobalConfig();
-    const migrations: Migration[] = [
-      new RequiredStatusChecksMigration(config, migratedConfig),
-    ];
-    migrations.forEach((migration) => {
-      migration.migrate();
-    });
+    applyMigrations(config, migratedConfig);
     for (const [key, val] of Object.entries(config)) {
       if (removedOptions.includes(key)) {
         delete migratedConfig[key];

lib/config/migrations/index.ts

@@ -0,0 +1,18 @@
+import { RenovateConfig } from '../types';
+import type { Migration } from './migration';
+import { RequiredStatusChecksMigration } from './required-status-checks-migration';
+
+export function applyMigrations(
+  originalConfig: RenovateConfig,
+  migratedConfig: RenovateConfig
+): RenovateConfig {
+  const migrations: Migration[] = [
+    new RequiredStatusChecksMigration(originalConfig, migratedConfig),
+  ];
+
+  for (const migration of migrations) {
+    migration.migrate();
+  }
+
+  return migratedConfig;
+}

lib/config/migrations/migration.ts

@@ -10,7 +10,7 @@ export abstract class Migration {
     this.migratedConfig = migratedConfig;
   }
 
-  abstract migrate(): RenovateConfig;
+  abstract migrate(): void;
 
   protected delete(property: string): void {
     delete this.migratedConfig[property];

lib/config/migrations/required-status-checks-migration.ts

@@ -1,14 +1,11 @@
-import { RenovateConfig } from '../types';
 import { Migration } from './migration';
 
 export class RequiredStatusChecksMigration extends Migration {
-  public migrate(): RenovateConfig {
+  public migrate(): void {
     this.delete('requiredStatusChecks');
 
     if (this.originalConfig.requiredStatusChecks === null) {
       this.migratedConfig.ignoreTests = true;
     }
-
-    return this.migratedConfig;
   }
 }