feat(manager/npm): use volta node pin as node version constraint

lib/modules/manager/npm/post-update/node-version.spec.ts

@@ -70,6 +70,31 @@ describe('modules/manager/npm/post-update/node-version', () => {
       );
       expect(res).toBe('^12.16.3');
     });
+
+    it('returns from package.json volta', async () => {
+      const res = await getNodeConstraint(
+        {},
+        [],
+        '',
+        new Lazy(() => Promise.resolve({ volta: { node: '14.17.0' } })),
+      );
+      expect(res).toBe('14.17.0');
+    });
+
+    it('prefers volta over engines', async () => {
+      const res = await getNodeConstraint(
+        {},
+        [],
+        '',
+        new Lazy(() =>
+          Promise.resolve({
+            volta: { node: '14.17.0' },
+            engines: { node: '^12.16.3' },
+          }),
+        ),
+      );
+      expect(res).toBe('14.17.0');
+    });
   });
 
   describe('getNodeUpdate()', () => {

lib/modules/manager/npm/post-update/node-version.ts

@@ -26,10 +26,24 @@ async function getNodeFile(filename: string): Promise<string | null> {
 async function getPackageJsonConstraint(
   pkg: LazyPackageJson,
 ): Promise<string | null> {
-  const constraint = (await pkg.getValue()).engines?.node;
-  if (constraint && semver.validRange(constraint)) {
-    logger.debug(`Using node constraint "${constraint}" from package.json`);
-    return constraint;
+  const pkgJson = await pkg.getValue();
+  if (pkgJson.volta?.node) {
+    const constraint = pkgJson.volta.node;
+    if (semver.validRange(constraint)) {
+      logger.debug(
+        `Using node constraint "${constraint}" from package.json volta`,
+      );
+      return constraint;
+    }
+  }
+  if (pkgJson.engines?.node) {
+    const constraint = pkgJson.engines.node;
+    if (semver.validRange(constraint)) {
+      logger.debug(
+        `Using node constraint "${constraint}" from package.json engines`,
+      );
+      return constraint;
+    }
   }
   return null;
 }