CI: Try to get Cygwin workflow working.

.github/workflows/test-cygwin.yml

@@ -11,7 +11,7 @@ jobs:
         python-minor-version: [7, 8]
         architecture: ["x86", "x86_64"]
 
-    timeout-minutes: 30
+    timeout-minutes: 40
 
     name: Python 3.${{ matrix.python-minor-version }} ${{ matrix.architecture }}
 
@@ -31,11 +31,18 @@ jobs:
             ImageMagick jpeg python3${{ matrix.python-minor-version }}-cffi
             python3${{ matrix.python-minor-version }}-devel
             python3${{ matrix.python-minor-version }}-numpy
+            python3${{ matrix.python-minor-version }}-cython liblapack-devel gcc-g++
             python3${{ matrix.python-minor-version }}-sip
             python3${{ matrix.python-minor-version }}-tkinter ghostscript
             libfreetype-devel libimagequant-devel libjpeg-devel liblcms2-devel
             libopenjp2-devel libraqm-devel libtiff-devel libwebp-devel libxcb-devel
             libxcb-xinerama0 netpbm perl qt5-devel-tools xorg-server-extra zlib-devel
+            subversion make
+
+      - name: Add Lapack to PATH
+        uses: egor-tensin/cleanup-path@v1
+        with:
+          dirs: 'C:\cygwin\bin;C:\cygwin\lib\lapack'
 
       - name: Build system information
         run: |
@@ -45,10 +52,22 @@ jobs:
         run: |
           bash.exe .ci/install.sh
 
+      - name: Install a different NumPy
+        run: |
+          bash.exe -c "python3.${{ matrix.python-minor-version }} -m pip install -U 'numpy!=1.21.*'"
+
+      - name: Check imports
+        run: |
+          bash.exe -c "python3.${{ matrix.python-minor-version }} -c 'import numpy as np; print(np.__version__)'"
+
       - name: Build
         run: |
           bash.exe .ci/build_cygwin.sh
 
+      - name: Rebase dlls
+        run: |
+          bash.exe -c '/usr/bin/rebase --database $(find /usr{,/local}/lib/python3.${{ matrix.python-minor-version }}/site-packages src/PIL ${HOME}/.local/lib/ /usr/lib/lapack /usr/bin -name \*.dll -o -name \*.exe)'
+
       - name: Test
         run: |
           bash.exe xvfb-run -s '-screen 0 1024x768x24' .ci/test.sh
@@ -56,7 +75,7 @@ jobs:
       - name: Prepare to upload errors
         if: failure()
         run: |
-          mkdir -p Tests/errors
+          dash.exe -c "mkdir -p Tests/errors"
 
       - name: Upload errors
         uses: actions/upload-artifact@v2