fix: don't try to install yarn 2 from npm (#7183)

as yarn 2 is local in the project and should be started by yarn 1 via yarn config file.
When using yarn2, installing latest yarn (v1) should work best

Co-authored-by: Michael Kriese <michael.kriese@visualon.de>

lib/manager/npm/post-update/yarn.ts

@@ -53,7 +53,7 @@ export async function generateLockFile(
       !isValidYarnRange || minVersion(yarnCompatibility).major === 1;
 
     let installYarn = 'npm i -g yarn';
-    if (isValidYarnRange) {
+    if (isYarn1 && isValidYarnRange) {
       installYarn += `@${quote(yarnCompatibility)}`;
     }