fix(ci): skip new-commit check on manual fixture release dispatches

[spencer-tb]

Description

#3100's new-commit check runs .github/scripts/check_new_commits.py from the checkout, but manual devnet releases check out inputs.branch, which can predate the script — the glamsterdam-devnet@v7.2.1 dispatch failed to spawn it. Gate the step on scheduled runs and default the run output to true for dispatches, which is all the script did for them anyway.

Related Issues or PRs

Introduced by #3100.

Checklist

• Ran fast static checks to avoid CI fails, see Code Standards & Verifying Changes: just static
• PR title has the form <type>(<area>): <title>, where <type> and <area> come from an appropriate C-<type>, respectively A-<area>, label. The title should match the target squash commit message.

Cute Animal Picture

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.39%. Comparing base (9e9bf90) to head (69fcc6e).

Additional details and impacted files

@@               Coverage Diff                @@
##           forks/amsterdam    #3202   +/-   ##
================================================
  Coverage            93.39%   93.39%           
================================================
  Files                  624      624           
  Lines                37014    37014           
  Branches              3386     3386           
================================================
  Hits                 34570    34570           
  Misses                1671     1671           
  Partials               773      773           

Flag	Coverage Δ
unittests	93.39% <ø> (ø)

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