Fix image stuttering (#3035)

* Fix image stuttering.

* Fix docker publishing for PRs

* Write tests for new square parameter.

* Simplify code for createImage.

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Co-authored-by: Deluan Quintão <deluan@navidrome.org>

server/subsonic/media_retrieval_test.go

@@ -257,7 +257,7 @@ type fakeArtwork struct {
 	recvSize int
 }
 
-func (c *fakeArtwork) GetOrPlaceholder(_ context.Context, id string, size int) (io.ReadCloser, time.Time, error) {
+func (c *fakeArtwork) GetOrPlaceholder(_ context.Context, id string, size int, square bool) (io.ReadCloser, time.Time, error) {
 	if c.err != nil {
 		return nil, time.Time{}, c.err
 	}