Speed-up Nx GitHub Actions by avoiding fetching entire git history

[kopach]

Background / Motivation

Nx docs and starter workflows currently suggest fetching entire git history every time:

- uses: actions/checkout@v4
  with:
    fetch-depth: 0   # 👈 Fetch entire history so `nx affected` can diff

For large, long-lived monorepos, this step alone can add some time to every CI run because it clones the full commit history and all tags.

Yet nx affected only needs (correct me if I'm wrong here):

1. The current commit (already available with default checkout depth 1).

2. A single base commit (e.g. origin/main) to diff against.

Fetching the entire DAG is overkill in 99 % of PR builds.

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Proposed usage/change

Replace fetch-depth: 0 with the default shallow clone (depth 1) plus one extra shallow fetch for the base branch:

- name: Checkout current commit (depth 1 by default)
  uses: actions/checkout@v4

- name: Fetch base branch for Nx diff (shallow)
  run: |
    git fetch --depth=1 origin ${{ env.CI_BASE_REF || 'main' }}:refs/remotes/origin/main

Then run Nx:

- name: Run affected targets
  run: npx nx affected --base=origin/main --head=HEAD

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Please let me know what do you think and whether my assumptions are correct also for corner cases