fix(gc) - fix the chunk_tail <= tail invariant

[wacban]

According to this line in the storage checker, the chunk tail should always be less or equal than the tail:

nearcore/chain/chain/src/store_validator/validate.rs

Line 146 in 99ecfa4

if chunk_tail > tail {

This invariant is broken, I'm guessing since #12025 as shown by nayduck gc test failing at this check:
https://nayduck.nearone.org/#/test/108874 - test1 stderr last line

This is a simple mitigation but I'm not 100% sure if correct - please let me know if it makes sense or not.

Even if not entirely correct it should not cause any problems. At worst gc will attempt to clean a little bit more data that isn't there. I hope.

The only real change here is the added saturating_sub(1) to the line where we set the tail.

[codecov]

Codecov Report

Attention: Patch coverage is 75.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 71.76%. Comparing base (99ecfa4) to head (5690fdf).
Report is 5 commits behind head on master.

Files with missing lines	Patch %	Lines
chain/chain/src/chain.rs	75.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #12207      +/-   ##
==========================================
+ Coverage   71.69%   71.76%   +0.06%     
==========================================
  Files         825      825              
  Lines      165834   165822      -12     
  Branches   165834   165822      -12     
==========================================
+ Hits       118902   118995      +93     
+ Misses      41751    41631     -120     
- Partials     5181     5196      +15     

Flag	Coverage Δ
backward-compatibility	0.17% <0.00%> (+<0.01%)	⬆️
db-migration	0.17% <0.00%> (+<0.01%)	⬆️
genesis-check	1.26% <0.00%> (+<0.01%)	⬆️
integration-tests	38.93% <75.00%> (+0.08%)	⬆️
linux	71.43% <75.00%> (+0.05%)	⬆️
linux-nightly	71.33% <75.00%> (+0.06%)	⬆️
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pytests	1.57% <0.00%> (+<0.01%)	⬆️
sanity-checks	1.38% <0.00%> (+<0.01%)	⬆️
unittests	65.51% <0.00%> (+0.14%)	⬆️
upgradability	0.21% <0.00%> (+<0.01%)	⬆️

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[Longarithm]

That's move in the right direction. To be 100% correct, I think we need to take chunks from new_tail instead of prev_block. This is because previous impl assumed that they are the same, now it is not the case.