fix: dont reset vault state on handover retry

[dandanlen]

I think this should also go into the 0.9 release.

It's a change that is pending in PR #3909 (Thanks @syan095)

Not including this means that key handovers can't recover properly from failures.

[codecov]

Codecov Report

Merging #3988 (773b03c) into release/0.9 (6fc28e6) will decrease coverage by 0%.
The diff coverage is 100%.

@@             Coverage Diff             @@
##           release/0.9   #3988   +/-   ##
===========================================
- Coverage           72%     72%   -0%     
===========================================
  Files              366     366           
  Lines            56869   56862    -7     
  Branches         56869   56862    -7     
===========================================
- Hits             41023   41013   -10     
- Misses           13760   13766    +6     
+ Partials          2086    2083    -3     

Files Changed	Coverage Δ
state-chain/pallets/cf-validator/src/lib.rs	74% <100%> (-<1%)	⬇️

... and 3 files with indirect coverage changes

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