fix(TemplateManager): Make sure TemplateFolder is a Folder

[solracsf]

• Resolves: [Bug]: Fail to create new files because of Call to undefined method OC\\Files\\Node\\File::searchByMime() [Cause: user templateDirectory pointed at a file] #49436

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)

[joshtrichards]

LOL I just wrote basically the same code and was about to shoot over the PR:

	private function getTemplateFolder(): Node {
		if ($this->getTemplatePath() !== '') {
			$userTemplateFolder = $this->rootFolder->getUserFolder($this->userId)->get($this->getTemplatePath());
			if ($userTemplateFolder->getType() === \OCP\Files\FileInfo::TYPE_FOLDER) {
				return $userTemplateFolder;
			}
		}
		throw new NotFoundException();
	}

Both re-trigger the new template folder setup setting (good). I didn't make the exception message more verbose though. Since it's caught silently when used in getTemplateFiles() I think re-triggering the Create new template folder option is enough (but won't hurt!).

[joshtrichards]

Tested/works.

[solracsf]

I didn't make the exception message more verbose though.

I've added a separate log line instead, could help when user expects something but get nothing and can't understand why.