Make build workflow job names more descriptive

Add `name` keys to the `test`, `build`, and `test-build` jobs that are
both more descriptive and include the Python version from the job's
matrix. This will produce consistent and more helpful job names in the
GitHub Actions log in the GitHub web UI.

.github/workflows/build.yml

@@ -103,6 +103,7 @@ jobs:
         uses: mxschmitt/action-tmate@v3
         if: env.RUN_TMATE
   test:
+    name: test source - py${{ matrix.python-version }}
     runs-on: ${{ matrix.os }}
     strategy:
       fail-fast: false
@@ -195,6 +196,7 @@ jobs:
         uses: mxschmitt/action-tmate@v3
         if: env.RUN_TMATE
   build:
+    name: build wheel - py${{ matrix.python-version }}
     needs:
       - lint
       - test
@@ -248,6 +250,7 @@ jobs:
         uses: mxschmitt/action-tmate@v3
         if: env.RUN_TMATE
   test-build:
+    name: test built wheel - py${{ matrix.python-version }}
     needs:
       - build
     runs-on: ${{ matrix.os }}