feat(config): set groupSingleUpdates=false by default (#44168)

* feat(config): set `groupSingleUpdates=false` by default

Although it didn't seem like this may be a breaking change when we
introduced this[0], there have been a number of follow-up Discussions
reported that have indicated there has been some breakage from the
changes.

Instead of continually fixing forward, we can revert this back to an
opt-in feature.

Once it's stable, we can look at re-enabling it (most likely in a major
release, unless we're confident no breakage should occur).

[0]: #43629 (comment)

* fixup! feat(config): set `groupSingleUpdates=false` by default

Author: jamietanna

docs/usage/configuration-options.md

@@ -2032,7 +2032,8 @@ For example, to group all non-major devDependencies updates together into a sing
 
 ## `groupSingleUpdates`
 
-For example, you can set it to `false` if you prefer individual dependency names in PR titles when only one update is in the group.
+!!! note
+  This option was [recently made opt-in, instead of opt-out](https://github.com/renovatebot/renovate/pull/44168).
 
 ## `groupSlug`
 

lib/config/options/index.ts

@@ -2617,7 +2617,7 @@ const options: Readonly<RenovateOptions>[] = [
     description:
       'Apply group settings even when the group contains only one update.',
     type: 'boolean',
-    default: true,
+    default: false,
     cli: false,
     env: false,
   },

lib/workers/repository/updates/generate.spec.ts

@@ -28,7 +28,7 @@ beforeEach(() => {
 
 describe('workers/repository/updates/generate', () => {
   describe('generateBranchConfig()', () => {
-    it('groups single upgrade by default', () => {
+    it('does not group single upgrade by default', () => {
       const { groupSingleUpdates } = getConfig();
       const branch = [
         {
@@ -47,10 +47,10 @@ describe('workers/repository/updates/generate', () => {
         },
       ] satisfies BranchUpgradeConfig[];
       const res = generateBranchConfig(branch);
-      expect(res.groupName).toBe('some-group');
-      expect(res.isGroup).toBeTrue();
-      expect(res.recreateClosed).toBeTrue();
-      expect(res.commitMessageExtra).toBeUndefined();
+      expect(res.groupName).toBeUndefined();
+      expect(res.isGroup).toBeUndefined();
+      expect(res.recreateClosed).toBeFalse();
+      expect(res.commitMessageExtra).toEqual('to 1.2.3');
     });
 
     it('groups single upgrade across multiple files', () => {