Auto merge of #13317 - Urgau:improve-ci, r=<try>

Improve GitHub Actions CI config

This pull request improves Cargo CI by:
 1. Explicitly listing the branches the main CI should be run on (to avoid running on unwanted branches, particularly in forks)
 2. By adding a [concurrency](https://docs.github.com/en/actions/using-jobs/using-concurrency) config so that only one "CI" runs for each "group" (one by PR), very inspired by rust-lang/rust [one](https://github.com/rust-lang/rust/blob/c485ee71477a29041895c47cc441b364670f3772/.github/workflows/ci.yml#L35)
 3. By making all the jobs run only if triggered from this repository (to avoid having forks unnecessarily run CI jobs)
 4. By making all the checkouts take `fetch-depth: 2` like done in [rust-lang/rust](https://github.com/rust-lang/rust/blob/c485ee71477a29041895c47cc441b364670f3772/.github/workflows/ci.yml#L452-L455) (to avoid unnecessary work, saves bandwidth and maybe a bit of time)

The main motivation for this PR was (at first) to make the CI jobs not run on forks since it's a waste of CI resources as well as always failing (like [this](https://github.com/Urgau/cargo/actions/runs/7567435677/job/20606586124)); but after looking at the `main.yml` config I took the opportunity to improve the situation by using rust-lang/rust [ci.yml](https://github.com/rust-lang/rust/blob/master/.github/workflows/ci.yml) as reference.

Author: bors

.github/workflows/main.yml

@@ -1,9 +1,14 @@
 name: CI
 on:
   push:
-    branches-ignore: [master]
+    branches:
+      - auto-cargo
+      - try
+      - automation/bors/try
+      - "rust-**"
   pull_request:
-    branches: ['*']
+    branches:
+      - "**"
 
 defaults:
   run:
@@ -12,6 +17,10 @@ defaults:
 permissions:
   contents: read
 
+concurrency:
+  group: "${{ github.workflow }}-${{ (github.ref == 'refs/heads/try' && github.sha) || github.ref }}"
+  cancel-in-progress: true
+
 jobs:
   success:
     permissions:
@@ -53,6 +62,7 @@ jobs:
   # Check Code style quickly by running `rustfmt` over all code
   rustfmt:
     runs-on: ubuntu-latest
+    if: "github.repository == 'rust-lang/cargo'"
     steps:
     - uses: actions/checkout@v4
     - run: rustup update stable && rustup default stable
@@ -62,6 +72,7 @@ jobs:
   # Ensure there are no clippy warnings
   clippy:
     runs-on: ubuntu-latest
+    if: "github.repository == 'rust-lang/cargo'"
     steps:
       - uses: actions/checkout@v4
       - run: rustup update stable && rustup default stable
@@ -78,13 +89,15 @@ jobs:
   # Ensure Cargo.lock is up-to-date
   lockfile:
     runs-on: ubuntu-latest
+    if: "github.repository == 'rust-lang/cargo'"
     steps:
       - uses: actions/checkout@v4
       - run: rustup update stable && rustup default stable
       - run: cargo update -p cargo --locked
 
   check-version-bump:
     runs-on: ubuntu-latest
+    if: "github.repository == 'rust-lang/cargo'"
     env:
       BASE_SHA: ${{ github.event.pull_request.base.sha }}
       HEAD_SHA: ${{ github.event.pull_request.head.sha != '' && github.event.pull_request.head.sha || github.sha  }}
@@ -108,6 +121,7 @@ jobs:
       CARGO_PROFILE_TEST_DEBUG: 1
       CARGO_INCREMENTAL: 0
       CARGO_PUBLIC_NETWORK_TESTS: 1
+    if: "github.repository == 'rust-lang/cargo'"
     strategy:
       matrix:
         include:
@@ -191,13 +205,15 @@ jobs:
 
   resolver:
     runs-on: ubuntu-latest
+    if: "github.repository == 'rust-lang/cargo'"
     steps:
     - uses: actions/checkout@v4
     - run: rustup update stable && rustup default stable
     - run: cargo test -p resolver-tests
 
   test_gitoxide:
     runs-on: ubuntu-latest
+    if: "github.repository == 'rust-lang/cargo'"
     steps:
       - uses: actions/checkout@v4
       - run: rustup update --no-self-update stable && rustup default stable
@@ -210,6 +226,7 @@ jobs:
 
   build_std:
     runs-on: ubuntu-latest
+    if: "github.repository == 'rust-lang/cargo'"
     steps:
     - uses: actions/checkout@v4
     - run: rustup update nightly && rustup default nightly
@@ -220,6 +237,7 @@ jobs:
         CARGO_RUN_BUILD_STD_TESTS: 1
   docs:
     runs-on: ubuntu-latest
+    if: "github.repository == 'rust-lang/cargo'"
     steps:
     - uses: actions/checkout@v4
     - run: rustup update nightly && rustup default nightly
@@ -247,6 +265,7 @@ jobs:
 
   msrv:
     runs-on: ubuntu-latest
+    if: "github.repository == 'rust-lang/cargo'"
     steps:
     - uses: actions/checkout@v4
     - uses: taiki-e/install-action@cargo-hack