ci: use pip install instead of setup.py develop

This is the modern way apparently.

Author: indygreg

.github/workflows/pypy.yml

@@ -40,7 +40,6 @@ jobs:
 
       - name: Build
         run: |
-          python -m pip install --upgrade pip wheel
           python -m pip wheel -w wheelhouse .
 
   test:
@@ -87,7 +86,7 @@ jobs:
 
       - name: Build
         run: |
-          python setup.py develop
+          python -m pip install -e .
 
       - name: Test
         run: |

.github/workflows/test.yml

@@ -58,12 +58,12 @@ jobs:
       - name: Build (Rust)
         if: matrix.arch == 'x64'
         run: |
-          python setup.py --rust-backend develop
+          python -m pip install --config-setting='--build-option=--rust-backend' -e .
 
       - name: Build (No Rust)
         if: matrix.arch != 'x64'
         run: |
-          python setup.py develop
+          python -m pip install -e .
 
       - name: Test C Backend
         run: |