Use https for links.

I thought I went over all these several years ago already, but
apparently not or maybe back then not all websites were HTTPS-ready. Now
they are.

doc/python/conf.py

@@ -267,7 +267,7 @@ PAGE_HEADER = """
 
 FINE_PRINT = """
 | Magnum Python docs. Part of the `Magnum project <https://magnum.graphics/>`_,
-  copyright © `Vladimír Vondruš <http://mosra.cz/>`_ and contributors, 2010--2025.
+  copyright © `Vladimír Vondruš <https://mosra.cz/>`_ and contributors, 2010--2025.
 | Generated by `m.css Python doc generator <https://mcss.mosra.cz/documentation/python/>`_.
   Contact the team via `GitHub <https://github.com/mosra/magnum>`_,
   `Gitter <https://gitter.im/mosra/magnum>`_,

package/ci/appveyor.yml

@@ -120,7 +120,7 @@ install:
 - 7z x v%PYBIND%.zip
 
 # SDL2
-- IF "%TARGET%" == "desktop" IF "%COMPILER:~0,4%" == "msvc" IF NOT EXIST %APPVEYOR_BUILD_FOLDER%\SDL2-devel-2.0.9-VC.zip appveyor DownloadFile http://www.libsdl.org/release/SDL2-devel-2.0.9-VC.zip
+- IF "%TARGET%" == "desktop" IF "%COMPILER:~0,4%" == "msvc" IF NOT EXIST %APPVEYOR_BUILD_FOLDER%\SDL2-devel-2.0.9-VC.zip appveyor DownloadFile https://www.libsdl.org/release/SDL2-devel-2.0.9-VC.zip
 - IF "%TARGET%" == "desktop" IF "%COMPILER:~0,4%" == "msvc" 7z x SDL2-devel-2.0.9-VC.zip && ren SDL2-2.0.9 SDL
 
 # GLFW