CI Linux: installing tkinter-gl from workflows/linux.yml since versio…

…n 1.0a2 isn't picked up otherwise.

.github/workflows/linux.yml

@@ -30,7 +30,8 @@ jobs:
             pip install --pre --extra-index-url https://test.pypi.org/simple cypari &&
             pip install git+https://github.com/3-manifolds/PLink &&
             pip install git+https://github.com/3-manifolds/snappy_manifolds &&
-            pip install git+https://github.com/3-manifolds/Spherogram
+            pip install git+https://github.com/3-manifolds/Spherogram &&
+            pip install git+https://github.com/3-manifolds/tkinter_gl
           CIBW_REPAIR_WHEEL_COMMAND_LINUX: auditwheel repair --strip -w {dest_dir} {wheel}
           CIBW_TEST_COMMAND: python -m snappy.test --skip-modern-opengl