fix(previews): lower log level when cached preview isn't found

Since this PR #52221 was implemented, the log file has been flooded with warnings stating, "Cached preview not found for file; generating a new preview." This appears to be more of an informational message rather than a warning. This PR will change it from warning to debug

Original PR
#52221

Signed-off-by: AndyXheli <andyxheli@gmail.com>

lib/private/Preview/Generator.php

@@ -165,7 +165,7 @@ class Generator {
 						$maxPreviewImage = $this->helper->getImage($maxPreview);
 					}
 
-					$this->logger->warning('Cached preview not found for file {path}, generating a new preview.', ['path' => $file->getPath()]);
+					$this->logger->debug('Cached preview not found for file {path}, generating a new preview.', ['path' => $file->getPath()]);
 					$preview = $this->generatePreview($previewFolder, $maxPreviewImage, $width, $height, $crop, $maxWidth, $maxHeight, $previewVersion, $cacheResult);
 					// New file, augment our array
 					$previewFiles[] = $preview;