gh-40448: Replace ci-linux-incremental by ci-linux
    
<!-- ^ Please provide a concise and informative title. -->
<!-- ^ Don't put issue numbers in the title, do this in the PR
description below. -->
<!-- ^ For example, instead of "Fixes #12345" use "Introduce new method
to calculate 1 + 2". -->
<!-- v Describe your changes below in detail. -->
<!-- v Why is this change required? What problem does it solve? -->
<!-- v If this PR resolves an open issue, please link to it here. For
example, "Fixes #12345". -->

The incremental runs are supposed to test package updates - however,
exactly in those situations, they are not working since the rebuilt
sagelib is not linking correctly against the new versions. For example,
in the flint update #40259, we get
>   [sagemath_doc_html-none]   [spkg-install]     from sage.rings import
complex_interval, integer
  [sagemath_doc_html-none]   [spkg-install] ImportError: libflint.so.20:
cannot open shared object file: No such file or directory

https://github.com/sagemath/sage/actions/runs/15979364834/job/4507007300
7?pr=40259#step:11:4686

For this reason, the incremental runs are replaced here by the build-
from-zero runs. Those are a bit slower but more reliable.

### :memo: Checklist

<!-- Put an `x` in all the boxes that apply. -->

- [ ] The title is concise and informative.
- [ ] The description explains in detail what this PR is about.
- [ ] I have linked a relevant issue or discussion.
- [ ] I have created tests covering the changes.
- [ ] I have updated the documentation and checked the documentation
preview.

### :hourglass: Dependencies

<!-- List all open PRs that this PR logically depends on. For example,
-->
<!-- - #12345: short description why this is a dependency -->
<!-- - #34567: ... -->
    
URL: #40448
Reported by: Tobias Diez
Reviewer(s): Dima Pasechnik

Author: Release Manager

.github/workflows/build.yml

@@ -35,7 +35,7 @@ concurrency:
 #
 # each build Sage:
 #
-#  - incrementally starting from a Docker image that ci-linux.yml
+#  - incrementally starting from a Docker image that ci-distro.yml
 #    publishes on each development release to ghcr.io,
 #  - orchestrated using a tox-generated Dockerfile,
 #  - using https://github.com/marketplace/actions/build-and-push-docker-images,

.github/workflows/ci-linux.yml renamed to .github/workflows/ci-distro.yml

@@ -1,7 +1,7 @@
-name: CI Linux
+name: CI (Distro)
 
-## This GitHub Actions workflow runs SAGE_ROOT/tox.ini with selected environments,
-## whenever a tag is pushed.
+## This GitHub Actions workflow builds and tests sage with selected environments,
+## whenever a tag is pushed or a pull request changes relevant build files.
 ##
 ## It builds and checks some sage spkgs as defined in TARGETS.
 ##
@@ -14,9 +14,18 @@ name: CI Linux
 ## After all jobs have finished (or are canceled) and a short delay,
 ## tar files of all logs are made available as "build artifacts".
 
-#on: [push, pull_request]
-
 on:
+  pull_request:
+    paths:
+      - '.github/workflows/ci-distro.yml'
+      - 'build/pkgs/**'
+      - 'configure.ac'
+      - '!build/pkgs/sage_conf/**'
+      - '!build/pkgs/sage_docbuild/**'
+      - '!build/pkgs/sage_setup/**'
+      - '!build/pkgs/sage_sws2rst/**'
+      - '!build/pkgs/sagelib/**'
+      - '!build/pkgs/sagemath_*/**'
   push:
     tags:
       - '*'
@@ -31,6 +40,11 @@ env:
 permissions:
   packages: write
 
+concurrency:
+  # Cancel previous runs of this workflow for the same branch
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
 jobs:
   minimal:
     if: ${{ success() || failure() }}

.github/workflows/ci-linux-incremental.yml

@@ -1003,7 +1003,7 @@ on every release tag.
 
 This is defined in the files
 
-- :sage_root:`.github/workflows/ci-linux.yml`
+- :sage_root:`.github/workflows/ci-distro.yml`
   (which calls :sage_root:`.github/workflows/docker.yml`) and
 
 - :sage_root:`.github/workflows/ci-macos.yml`