Allow merge commits

[nick-mobilecoin]

Previously merge commits were disallowed. When using stacked PRs, if the
initial PR uses a squash merge, git and github loose the information to
associate the initial commits in subsequent PRs as belonging to the
initial PR. This results in github saying there are merge conflicts.
Using merge commits allows github to better keep track of which commits
are unique to each PR.

Motivation

[nick-mobilecoin]

Current dependencies on/for this PR:

• Allow merge commits #17 👈
• main

This stack of pull requests is managed by Graphite.

[github-actions]

❌ Unreviewed dependencies found

Crate	Version	Reviews (N/2)	LoC	Left-Pad Index	Geiger	Flags
clap	4.2.5	0	77	500	0	____
hex_fmt	0.3.0	0	168	42	0	____
displaydoc	0.2.3	0	409	68	24	____
sha2	0.10.6	0	1061	114	204	____
textwrap	0.16.0	0	2234	76	0	____
nom	7.1.3	0	10471	33	40	____

[codecov]

Codecov Report

Merging #17 (f67c064) into main (871334e) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main      #17   +/-   ##
=======================================
  Coverage   79.42%   79.42%           
=======================================
  Files           2        2           
  Lines         243      243           
=======================================
  Hits          193      193           
  Misses         50       50           

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