fix(Makefile): Graceful cargo-nextest install

[refcell]

Addresses #4008.

This PR is a very simple addition to the Makefile to install the cargo-nextest bin prior to executing unit tests with cargo nextest ...

[mattsse]

this will display a message if already installed,

I think we can live with that, wdyt @onbjerg ?

[codecov]

Codecov Report

Merging #4009 (8e95e19) into main (dee14c7) will decrease coverage by 0.05%.
Report is 2 commits behind head on main.
The diff coverage is n/a.

see 12 files with indirect coverage changes

Flag	Coverage Δ
integration-tests	16.23% <ø> (-0.03%)	⬇️
unit-tests	64.14% <ø> (-0.05%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Components	Coverage Δ
reth binary	25.63% <ø> (-0.07%)	⬇️
blockchain tree	83.04% <ø> (ø)
pipeline	90.03% <ø> (ø)
storage (db)	74.30% <ø> (ø)
trie	94.70% <ø> (ø)
txpool	45.40% <ø> (-0.61%)	⬇️
networking	77.49% <ø> (-0.03%)	⬇️
rpc	58.37% <ø> (+0.01%)	⬆️
consensus	63.51% <ø> (ø)
revm	33.10% <ø> (ø)
payload builder	6.58% <ø> (ø)
primitives	88.04% <ø> (-0.02%)	⬇️

[rkrasiuk]

supportive, pending @onbjerg

[onbjerg]

Seems okay