s3: return InvalidArgument for malformed x-amz-content-sha256

A header value that decodes to neither 32-byte hex nor base64 is a
malformed argument, not a hash mismatch.

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

weed/s3api/s3api_put_object_helper.go

@@ -42,7 +42,7 @@ func getRequestDataReader(s3a *S3ApiServer, r *http.Request) (io.ReadCloser, s3e
 
 	expected, valid := expectedContentSha256(r)
 	if !valid {
-		return nil, s3err.ErrContentSHA256Mismatch
+		return nil, s3err.ErrInvalidArgument
 	}
 	if expected != nil && dataReader != nil {
 		if r.ContentLength == 0 {

weed/s3api/s3api_put_object_helper_test.go

@@ -299,6 +299,12 @@ func TestGetRequestDataReaderEmptyBodyHash(t *testing.T) {
 		t.Fatalf("empty body with wrong hash: code=%v", code)
 	}
 
+	malformed := httptest.NewRequest("PUT", "/b/o", strings.NewReader("x"))
+	malformed.Header.Set("X-Amz-Content-Sha256", "nothex")
+	if _, code := getRequestDataReader(s3a, malformed); code != s3err.ErrInvalidArgument {
+		t.Fatalf("malformed sha256 header: code=%v", code)
+	}
+
 	emptySum := sha256.Sum256(nil)
 	match := httptest.NewRequest("PUT", "/b/dir/", http.NoBody)
 	match.Header.Set("X-Amz-Content-Sha256", hex.EncodeToString(emptySum[:]))