[docs] Update broken links in docs

[StrikerRUS]

https://github.com/microsoft/LightGBM/runs/6736962389?check_suite_focus=true

URL        `http://iweb.dl.sourceforge.net/project/mingw-w64/Toolchains%20targetting%20Win32/Personal%20Builds/mingw-builds/installer/mingw-w64-install.exe'
Name       `this'
Parent URL file:///home/runner/work/LightGBM/LightGBM/docs/_build/html/GPU-Windows.html, line 149, col 47
Real URL   http://iweb.dl.sourceforge.net/project/mingw-w64/Toolchains%20targetting%20Win32/Personal%20Builds/mingw-builds/installer/mingw-w64-install.exe
Check time 120.214 seconds
Result     Error: ConnectionError: HTTPConnectionPool(host='iweb.dl.sourceforge.net', port=80): Max retries exceeded with url: /project/mingw-w64/Toolchains%20targetting%20Win32/Personal%20Builds/mingw-builds/installer/mingw-w64-install.exe (Caused by NewCon...
URL        `https://mirror.linux-ia64.org/fedora/linux/releases/32/Everything/x86_64/os/Packages/m/mingw64-boost-static-1.66.0-6.fc32.noarch.rpm'
Name       `Prebuilt Boost x86_64'
Parent URL file:///home/runner/work/LightGBM/LightGBM/docs/_build/html/GPU-Windows.html, line 175, col 14
Real URL   https://mirror.linux-ia64.org/fedora/linux/releases/32/Everything/x86_64/os/Packages/m/mingw64-boost-static-1.66.0-6.fc32.noarch.rpm
Check time 1.325 seconds
Result     Error: 404 Not Found
URL        `https://mirror.linux-ia64.org/fedora/linux/releases/32/Everything/x86_64/os/Packages/m/mingw32-boost-static-1.66.0-6.fc32.noarch.rpm'
Name       `Prebuilt Boost i686'
Parent URL file:///home/runner/work/LightGBM/LightGBM/docs/_build/html/GPU-Windows.html, line 175, col 213
Real URL   https://mirror.linux-ia64.org/fedora/linux/releases/32/Everything/x86_64/os/Packages/m/mingw32-boost-static-1.66.0-6.fc32.noarch.rpm
Check time 2.091 seconds
Result     Error: 404 Not Found

[jameslamb]

Thanks!

[github-actions]

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