pip with --no-build-isolation (also in Makefile)

.github/workflows/ci-sage.yml

@@ -107,7 +107,7 @@ jobs:
         choco install make autoconf gcc-core gcc-g++ python3${{ matrix.python-version }}-devel --source cygwin
     - name: install dependencies
       run: |
-        C:\\tools\\cygwin\\bin\\bash -l -x -c 'export PATH=/usr/local/bin:/usr/bin && cd $(cygpath -u "$GITHUB_WORKSPACE") && python3.${{ matrix.python-version }} -m pip install -U setuptools cysignals Cython Sphinx flake8'
+        C:\\tools\\cygwin\\bin\\bash -l -x -c 'export PATH=/usr/local/bin:/usr/bin && cd $(cygpath -u "$GITHUB_WORKSPACE") && python3.${{ matrix.python-version }} -m pip install -U --no-build-isolation setuptools cysignals Cython Sphinx flake8'
     - name: install
       run: |
         C:\\tools\\cygwin\\bin\\bash -l -x -c 'export PATH=/usr/local/bin:/usr/bin && cd $(cygpath -u "$GITHUB_WORKSPACE") && python3.${{ matrix.python-version }} setup.py build_ext -i'
@@ -221,7 +221,7 @@ jobs:
     - name: Install dependencies
       run: |
           python -m pip install --upgrade pip
-          pip install -U setuptools Cython Sphinx flake8
+          pip install -U --no-build-isolation setuptools Cython Sphinx flake8
     - name: Freeze pip
       run: |
           pip freeze
@@ -267,7 +267,7 @@ jobs:
     - name: Install dependencies
       run: |
           python -m pip install --upgrade pip
-          pip install -U setuptools Cython Sphinx flake8
+          pip install -U --no-build-isolation setuptools Cython Sphinx flake8
     - name: Freeze pip
       run: |
           pip freeze

Makefile

@@ -19,7 +19,7 @@ build: configure
 	$(PYTHON) setup.py build
 
 install: configure
-	$(PIP) install --no-index --ignore-installed --no-deps .
+	$(PIP) install --no-build-isolation --no-index --ignore-installed --no-deps .
 
 dist: configure
 	chmod -R go+rX-w .