Prevent ChannelForceClosed monitor update error after detecting spend

[wpaulino]

If we detected a spend for a channel onchain prior to handling its ChannelForceClosed monitor update, we'd log a concerning error message and return an error unnecessarily. The channel has already been closed, so handling the ChannelForceClosed monitor update at this point should be a no-op.

Fixes #2263.

[TheBlueMatt]

Let's also log in ChannelManager when we send the force-close-cause-theres-no-channel-for-a-channelmonitor force-close-update saying something about how we don't have a channel, it was probably closed before, but we're checking again.

[codecov-commenter]

Codecov Report

Patch coverage: 100.00% and project coverage change: -0.01 ⚠️

Comparison is base (e94647c) 91.50% compared to head (a33a1bc) 91.49%.

❗ Current head a33a1bc differs from pull request most recent head 1aeb821. Consider uploading reports for the commit 1aeb821 to get more accurate results

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Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2265      +/-   ##
==========================================
- Coverage   91.50%   91.49%   -0.01%     
==========================================
  Files         104      104              
  Lines       52087    52096       +9     
  Branches    52087    52096       +9     
==========================================
+ Hits        47660    47666       +6     
- Misses       4427     4430       +3     

Impacted Files	Coverage Δ
lightning/src/chain/channelmonitor.rs	94.84% <100.00%> (+0.01%)	⬆️
lightning/src/ln/channelmanager.rs	87.23% <100.00%> (+<0.01%)	⬆️

... and 1 file with indirect coverage changes

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