sagemathgh-39369: Test pip editable install with meson
    
Tests pip editable install with meson on GitHub Actions.

This uncovers several failing tests, which are fixed by (see
dependencies below)

Note: review is hard because of the large number of dependencies. It is
probably easier to look only in `.github` folder.


### 📝 Checklist

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

- [x] The title is concise and informative.
- [x] The description explains in detail what this PR is about.
- [x] I have linked a relevant issue or discussion.

### ⌛ Dependencies


- sagemath#39423
- sagemath#39498
- sagemath#39494
- sagemath#39424
- sagemath#39275
- sagemath#39499
    
URL: sagemath#39369
Reported by: user202729
Reviewer(s): Tobias Diez, user202729

Author: Release Manager

.github/workflows/ci-meson.yml

@@ -16,14 +16,21 @@ concurrency:
 
 jobs:
   test:
-    name: Conda (${{ matrix.os }}, Python ${{ matrix.python }})
+    name: Conda (${{ matrix.os }}, Python ${{ matrix.python }}${{ matrix.editable && ', editable' || '' }})
     runs-on: ${{ matrix.os }}-latest
 
     strategy:
       fail-fast: false
       matrix:
         os: [ubuntu]
         python: ['3.11', '3.12']
+        editable:
+          ${{ fromJson(github.event_name == 'pull_request' && '[false]' || '[false, true]') }}
+        include:
+          # one additional editable run in pull_request, this has no effect if not pull_request
+          - os: ubuntu
+            python: 3.12
+            editable: true
 
     steps:
       - uses: actions/checkout@v4
@@ -70,7 +77,7 @@ jobs:
           export CC="ccache $CC"
           export CXX="ccache $CXX"
           # Use --no-deps and pip check below to verify that all necessary dependencies are installed via conda
-          pip install --no-build-isolation --no-deps --config-settings=builddir=builddir . -v
+          pip install --no-build-isolation --no-deps --config-settings=builddir=builddir ${{ matrix.editable && '--editable' || '' }} . -v
 
       - name: Check update-meson
         # this step must be after build, because meson.build creates a number of __init__.py files
@@ -93,12 +100,14 @@ jobs:
         shell: bash -l {0}
         run: |
           # We don't install sage_setup, so don't try to test it
-          rm -R ./src/sage_setup/
+          # If editable then deleting the directory will cause sage to detect rebuild, which will cause ninja to fail
+          # so we don't delete the directory in this case
+          ${{ matrix.editable && 'true' || 'rm -R ./src/sage_setup/' }}
           ./sage -t --all -p4 --format github
 
       - name: Upload log
         uses: actions/[email protected]
         if: failure()
         with:
-          name: ${{ runner.os }}-meson-${{ matrix.python }}-log
+          name: ${{ runner.os }}-meson-${{ matrix.python }}${{ matrix.editable && '-editable' || '' }}-log
           path: builddir/meson-logs/