base_attachment_storage: _register_hook do nothing if it is disabled

[leemannd]

When doing a migration and installing the module and having disabled the storage. I don't want the register hook to do anything.

[codecov-commenter]

Codecov Report

Merging #438 (d5e446b) into 16.0 (0d0ca60) will increase coverage by 0.92%. The diff coverage is 0.00%.

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@@            Coverage Diff             @@
##             16.0     #438      +/-   ##
==========================================
+ Coverage   36.05%   36.97%   +0.92%     
==========================================
  Files          33       33              
  Lines         760      760              
  Branches      106      106              
==========================================
+ Hits          274      281       +7     
+ Misses        480      471       -9     
- Partials        6        8       +2     

Files Changed	Coverage Δ
..._attachment_object_storage/models/ir_attachment.py	25.34% <0.00%> (+2.30%)	:arrow_up:

... and 1 file with indirect coverage changes

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[github-actions[bot]]

There hasn't been any activity on this pull request in the past 4 months, so it has been marked as stale and it will be closed automatically if no further activity occurs in the next 30 days. If you want this PR to never become stale, please ask a PSC member to apply the "no stale" label.

[leemannd]

Closing as I didn't receive any feedback