s3: fix --s3-no-head panic: reflect: Elem of invalid type s3.PutObjectInput

In

22abd785eb s3: implement reading and writing of metadata #111

The reading information of objects was refactored to use the
s3.HeadObjectOutput structure.

Unfortunately the code branch with `--s3-no-head` was not tested
otherwise this panic would have been discovered.

This shows that this is path is not integration tested, so this adds a
new integration test.

Fixes #6322

backend/s3/s3.go

@@ -4570,7 +4570,7 @@ func (o *Object) Update(ctx context.Context, in io.Reader, src fs.ObjectInfo, op
 	// uploaded properly. If size < 0 then we need to do the HEAD.
 	if o.fs.opt.NoHead && size >= 0 {
 		var head s3.HeadObjectOutput
-		structs.SetFrom(&head, req)
+		structs.SetFrom(&head, &req)
 		head.ETag = &md5sumHex // doesn't matter quotes are misssing
 		head.ContentLength = &size
 		// If we have done a single part PUT request then we can read these

backend/s3/s3_internal_test.go

@@ -67,8 +67,26 @@ func (f *Fs) InternalTestMetadata(t *testing.T) {
 	}
 }
 
+func (f *Fs) InternalTestNoHead(t *testing.T) {
+	ctx := context.Background()
+	// Set NoHead for this test
+	f.opt.NoHead = true
+	defer func() {
+		f.opt.NoHead = false
+	}()
+	contents := random.String(1000)
+	item := fstest.NewItem("test-no-head", contents, fstest.Time("2001-05-06T04:05:06.499999999Z"))
+	obj := fstests.PutTestContents(ctx, t, f, &item, contents, true)
+	defer func() {
+		assert.NoError(t, obj.Remove(ctx))
+	}()
+	// PutTestcontests checks the received object
+
+}
+
 func (f *Fs) InternalTest(t *testing.T) {
 	t.Run("Metadata", f.InternalTestMetadata)
+	t.Run("NoHead", f.InternalTestNoHead)
 }
 
 var _ fstests.InternalTester = (*Fs)(nil)