Adds newline to fastboot's CLI help

[brooksprumo]

Problem

I noticed the help text for fastboot (--use-snapshot-archives-at-startup) was missing a newline for "Specifying when-newest". Here's the current help text. I've added a (X) for the missing newline.

    --use-snapshot-archives-at-startup <use_snapshot_archives_at_startup>
            At startup, when should snapshot archives be extracted versus using what is already on disk? 
            Specifying "always" will always startup by extracting snapshot archives and disregard any snapshot-related
            state already on disk. Note that starting up from snapshot archives will incur the runtime costs associated
            with extracting the archives and rebuilding the local state. 
            Specifying "never" will never startup from snapshot archives and will only use snapshot-related state
            already on disk. If there is no state already on disk, startup will fail. Note, this will use the latest
            state available, which may be newer than the latest snapshot archive. (X) Specifying "when-newest" will use
            snapshot-related state already on disk unless there are snapshot archives newer than it. This can happen if
            a new snapshot archive is downloaded while the node is stopped. [default: always]  [possible values: always,
            never, when-newest]

Summary of Changes

Add the missing newline.

[mergify]

Backports to the beta branch are to be avoided unless absolutely necessary for fixing bugs, security issues, and perf regressions. Changes intended for backport should be structured such that a minimum effective diff can be committed separately from any refactoring, plumbing, cleanup, etc that are not strictly necessary to achieve the goal. Any of the latter should go only into master and ride the normal stabilization schedule. Exceptions include CI/metrics changes, CLI improvements and documentation updates on a case by case basis.

[mergify]

automerge label removed due to a CI failure

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (74fde2d) 81.8% compared to head (3061398) 81.8%.
Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master   #34712   +/-   ##
=======================================
  Coverage    81.8%    81.8%           
=======================================
  Files         824      824           
  Lines      222719   222719           
=======================================
+ Hits       182285   182305   +20     
+ Misses      40434    40414   -20