fix: add time to the sdk.Context used in PrepareProposal (backport #2515)

[mergify]

This is an automatic backport of pull request #2515 done by Mergify.
Cherry-pick of 9617549 has failed:

On branch mergify/bp/v1.x/pr-2515
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  (fix conflicts and run "git cherry-pick --continue")
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Changes to be committed:
	modified:   Makefile
	modified:   app/prepare_proposal.go
	new file:   app/test/prepare_proposal_context_test.go
	modified:   app/test/prepare_proposal_test.go
	modified:   app/test/process_proposal_test.go
	modified:   go.mod
	modified:   go.sum

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   app/test/fuzz_abci_test.go

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/github/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

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[codecov-commenter]

Codecov Report

Merging #2534 (b3408bf) into v1.x (10574fa) will decrease coverage by 0.01%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##             v1.x    #2534      +/-   ##
==========================================
- Coverage   20.36%   20.35%   -0.01%     
==========================================
  Files         138      138              
  Lines       15881    15885       +4     
==========================================
  Hits         3234     3234              
- Misses      12339    12343       +4     
  Partials      308      308              

Files Changed	Coverage Δ
app/prepare_proposal.go	0.00% <0.00%> (ø)