Install Pillow together with the rest of our CI deps (#1952)

We shouldn't assume how the user wants to install things.
In particular, `--break-system-packages` is egregious.

---------

Co-authored-by: Rangi <sylvie.oukaour+rangi42@gmail.com>

.github/workflows/testing.yml

@@ -95,9 +95,6 @@ jobs:
         continue-on-error: true
         run: |
           test/fetch-test-deps.sh
-      - name: Install test dependency dependencies
-        run: |
-          test/fetch-test-deps.sh --get-deps ${{ matrix.os }}
       - name: Run tests using our script
         if: matrix.buildsys == 'make'
         run: |
@@ -155,9 +152,6 @@ jobs:
         continue-on-error: true
         run: |
           test/fetch-test-deps.sh
-      - name: Install test dependency dependencies
-        run: |
-          test/fetch-test-deps.sh --get-deps macos
       - name: Run tests
         run: |
           ctest --test-dir build --schedule-random
@@ -216,9 +210,6 @@ jobs:
         continue-on-error: true
         run: |
           test/fetch-test-deps.sh
-      - name: Install test dependency dependencies
-        run: |
-          test/fetch-test-deps.sh --get-deps ${{ matrix.os }}
       - name: Run tests using CTest
         run: |
           ctest --test-dir build --schedule-random
@@ -277,6 +268,9 @@ jobs:
     steps:
       - name: Checkout repo
         uses: actions/checkout@v6
+      - name: Install test deps
+        run: |
+          .github/scripts/install_deps.sh windowsmingw
       - name: Retrieve binaries
         uses: actions/download-artifact@v8
         with:
@@ -309,9 +303,6 @@ jobs:
         continue-on-error: true
         run: |
           test/fetch-test-deps.sh
-      - name: Install test dependency dependencies
-        run: |
-          test/fetch-test-deps.sh --get-deps ${{ matrix.os }}
       - name: Run tests
         run: |
           test/run-tests.sh --os ${{ matrix.os }}