ci: always use constraints.txt

Let's ensure our setuptools constraint is honored everywhere.
Otherwise we get spammed with deprecation warnings and have to
reason about inconsistent behaviors.

Author: indygreg

.github/workflows/anaconda.yml

@@ -33,6 +33,8 @@ jobs:
           $CONDA/bin/conda create --yes --quiet --name env python=${{ matrix.py }}
 
       - name: Install Dependencies
+        env:
+          PIP_CONSTRAINT: 'ci/constraints.txt'
         run: |
           source $CONDA/bin/activate env
           $CONDA/bin/conda install --yes --quiet --name env conda-build pip
@@ -79,6 +81,8 @@ jobs:
           C:\Miniconda\condabin\conda.bat create --yes --quiet --name env python=${{ matrix.py }}
 
       - name: Install Dependencies
+        env:
+          PIP_CONSTRAINT: 'ci/constraints.txt'
         run: |
           C:\Miniconda\condabin\conda.bat install --yes --quiet --name env conda-build pip
           C:\Miniconda\envs\env\python.exe -m pip install --user --require-hashes -r ci/requirements.txt

.github/workflows/pypy.yml

@@ -39,6 +39,8 @@ jobs:
       - uses: actions/checkout@v4
 
       - name: Build
+        env:
+          PIP_CONSTRAINT: 'ci/constraints.txt'
         run: |
           python -m pip wheel -w wheelhouse .
 
@@ -81,10 +83,14 @@ jobs:
       - uses: actions/checkout@v4
 
       - name: Install Dependencies
+        env:
+          PIP_CONSTRAINT: 'ci/constraints.txt'
         run: |
           pip install --require-hashes -r ci/requirements.pypy.txt
 
       - name: Build
+        env:
+          PIP_CONSTRAINT: 'ci/constraints.txt'
         run: |
           python -m pip install -e .
 

.github/workflows/test.yml

@@ -75,6 +75,8 @@ jobs:
 
       - name: Install Dependencies
         shell: bash
+        env:
+          PIP_CONSTRAINT: 'ci/constraints.txt'
         run: |
           python -m pip install --require-hashes -r ci/requirements.txt
 
@@ -88,6 +90,8 @@ jobs:
 
       - name: Build (No Rust)
         if: matrix.arch != 'x64' || matrix.py == '3.13'
+        env:
+          PIP_CONSTRAINT: 'ci/constraints.txt'
         run: |
           python -m pip install -e .
 

.github/workflows/typing.yml

@@ -23,6 +23,8 @@ jobs:
           version: "0.4.29"
 
       - name: Install Dependencies
+        env:
+          PIP_CONSTRAINT: 'ci/constraints.txt'
         run: |
           uv venv --python ${{ matrix.py }} venv
           source venv/bin/activate

.github/workflows/wheel.yml

@@ -38,7 +38,7 @@ jobs:
 
       - name: Build Wheel
         run: |
-          docker run -e PYPATH=/opt/python/${{ matrix.py }} -e ZSTD_WARNINGS_AS_ERRORS=1 --rm -v `pwd`:/project quay.io/pypa/${{ matrix.image }} /project/ci/build-manylinux-wheel.sh
+          docker run -e PIP_CONSTRAINT=/project/ci/constraints.txt -e PYPATH=/opt/python/${{ matrix.py }} -e ZSTD_WARNINGS_AS_ERRORS=1 --rm -v `pwd`:/project quay.io/pypa/${{ matrix.image }} /project/ci/build-manylinux-wheel.sh
 
       - name: Upload Wheel
         uses: actions/upload-artifact@v4
@@ -65,6 +65,7 @@ jobs:
       CIBW_BUILD: ${{ matrix.py }}-*
       CIBW_BUILD_VERBOSITY: '1'
       CIBW_PRERELEASE_PYTHONS: '1'
+      PIP_CONSTRAINT: ci/constraints.txt
       ZSTD_WARNINGS_AS_ERRORS: '1'
     steps:
       - name: Set up Python
@@ -104,6 +105,7 @@ jobs:
           - 'arm64'
     runs-on: 'windows-2022'
     env:
+      PIP_CONSTRAINT: ci/constraints.txt
       ZSTD_WARNINGS_AS_ERRORS: '1'
     steps:
       - name: Set up Python