[appveyor] use different mirror for keyring

Default repo mirror is not available, changed to other one.

appveyor.yml

@@ -22,10 +22,10 @@ environment:
 
 install:
 # install new signing keyring
-#- c:\msys64\usr\bin\bash -lc "curl -O http://repo.msys2.org/msys/x86_64/msys2-keyring-r21.b39fb11-1-any.pkg.tar.xz"
-#- c:\msys64\usr\bin\bash -lc "curl -O http://repo.msys2.org/msys/x86_64/msys2-keyring-r21.b39fb11-1-any.pkg.tar.xz.sig"
-#- c:\msys64\usr\bin\bash -lc "pacman-key --verify msys2-keyring-r21.b39fb11-1-any.pkg.tar.xz.sig"
-#- c:\msys64\usr\bin\bash -lc "pacman --noconfirm -U msys2-keyring-r21.b39fb11-1-any.pkg.tar.xz"
+- c:\msys64\usr\bin\bash -lc "curl -O https://mirror.selfnet.de/msys2/msys/x86_64/msys2-keyring-r21.b39fb11-1-any.pkg.tar.xz"
+- c:\msys64\usr\bin\bash -lc "curl -O https://mirror.selfnet.de/msys2/msys/x86_64/msys2-keyring-r21.b39fb11-1-any.pkg.tar.xz.sig"
+- c:\msys64\usr\bin\bash -lc "pacman-key --verify msys2-keyring-r21.b39fb11-1-any.pkg.tar.xz.sig"
+- c:\msys64\usr\bin\bash -lc "pacman --noconfirm -U msys2-keyring-r21.b39fb11-1-any.pkg.tar.xz"
 # remove packages which can break build
 - c:\msys64\usr\bin\bash -lc "pacman --noconfirm -Rns gcc-fortran gcc mingw-w64-{i686,x86_64}-gcc-ada mingw-w64-{i686,x86_64}-gcc-objc"
 # update runtime