Allow to reuse modified objects on async_get

[bloodbare]

This PR fixes https://github.com/plone/guillotina/issues/1054

[codecov-io]

Codecov Report

Merging #1106 (5e09ee7) into master (620a468) will decrease coverage by 0.2%. The diff coverage is 98.3%.

@@           Coverage Diff            @@
##           master   #1106     +/-   ##
========================================
- Coverage    94.6%   94.5%   -0.1%     
========================================
  Files         348     367     +19     
  Lines       29798   31827   +2029     
========================================
+ Hits        28172   30048   +1876     
- Misses       1626    1779    +153     

Impacted Files	Coverage Δ
guillotina/db/transaction.py	90.4% <93.8%> (+0.1%)	:arrow_up:
guillotina/contrib/memcached/driver.py	92.2% <100.0%> (-<0.1%)	:arrow_down:
...uillotina/tests/memcached/test_memcached_driver.py	100.0% <100.0%> (ø)
guillotina/tests/test_transactions.py	100.0% <100.0%> (ø)
guillotina/contrib/pubsub/utility.py	84.8% <0.0%> (-2.1%)	:arrow_down:
guillotina/db/storages/pg.py	88.4% <0.0%> (-0.1%)	:arrow_down:
guillotina/response.py	88.0% <0.0%> (ø)
guillotina/languages.py	82.4% <0.0%> (ø)
guillotina/const.py	100.0% <0.0%> (ø)
guillotina/catalog/__init__.py	97.3% <0.0%> (ø)
... and 15 more