HPCGAP: Using Immutable on a mutable atomic component object returns a mutable result

[stevelinton]

I'm trying to construct a test for #3592 which will pass in the HPCGAP travis tests.
Deleting some irrelevant stuff, I get:

Observed behaviour

gap> foo := rec();;
gap> fam := NewFamily("FruitFamily");
<Family: "FruitFamily">
gap> Objectify(NewType(fam, IsMutable and IsAttributeStoringRep), foo);
<object>
gap> foo := Immutable(foo);
<object>
gap> IsMutable(foo);
true

Expected behaviour

Final line should be false

Copy and paste GAP banner (to tell us about your setup)

┌───────┐   HPC-GAP 4.10dev-2201-g52907f5 of today
 │  GAP  │   https://www.gap-system.org
 └───────┘   Architecture: x86_64-apple-darwin18.5.0-hpcgap64-kv7
             Maximum concurrent threads: 4
 Configuration:  gmp 6.1.2, Boehm GC

#W <<< This is an alpha release.      >>>
#W <<< Do not use for important work. >>>

 Loading the library and packages ...
Syntax warning: Unbound global variable in /Users/sal/GIT/gap/pkg/atlasrep/gap/utils.gi:44
        pos:= POSITION_FIRST_COMPONENT_SORTED( WidthUnicodeTable, ints[j] );
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 Packages:   AClib 1.3.1, Alnuth 3.1.0, AtlasRep 1.5.1, AutoDoc 2019.07.03, AutPGrp 1.10, CRISP 1.4.4, Cryst 4.1.18, CrystCat 1.1.8, CTblLib 1.2.2, FactInt 1.6.2, FGA 1.4.0, 
             GAPDoc 1.6.2, IRREDSOL 1.4, LAGUNA 3.9.2, Polenta 1.3.8, Polycyclic 2.14, PrimGrp 3.3.2, RadiRoot 2.8, ResClasses 4.7.1, SmallGrp 1.3, Sophus 1.24, SpinSym 1.5, 
             TomLib 1.2.7, TransGrp 2.0.4, utils 0.61
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