azure: Use msys2 20210604 installer for Windows build

MSYS2 Windows build started to fail since yesterday (Jun 21):

  checking keyring...
  checking package integrity...
  error: gcc-libs: signature from "David Macek <david.macek.0@gmail.com>" is unknown trust
  :: File /var/cache/pacman/pkg/gcc-libs-10.2.0-1-x86_64.pkg.tar.zst is corrupted (invalid or corrupted package (PGP signature)).
  error: gcc: signature from "David Macek <david.macek.0@gmail.com>" is unknown trust
  :: File /var/cache/pacman/pkg/gcc-10.2.0-1-x86_64.pkg.tar.zst is corrupted (invalid or corrupted package (PGP signature)).
  error: failed to commit transaction (invalid or corrupted package)
  Errors occurred, no packages were upgraded.

Switching to the latest installer (version 20210604) seems to fix it.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Tested-by: Tom Rini <trini@konsulko.com>
diff --git a/.azure-pipelines.yml b/.azure-pipelines.yml
index 35ab7f3..221e600 100644
--- a/.azure-pipelines.yml
+++ b/.azure-pipelines.yml
@@ -16,7 +16,7 @@
       vmImage: $(windows_vm)
     steps:
       - powershell: |
-          (New-Object Net.WebClient).DownloadFile("https://github.com/msys2/msys2-installer/releases/download/2020-07-20/msys2-base-x86_64-20200720.sfx.exe", "sfx.exe")
+          (New-Object Net.WebClient).DownloadFile("https://github.com/msys2/msys2-installer/releases/download/2021-06-04/msys2-base-x86_64-20210604.sfx.exe", "sfx.exe")
         displayName: 'Install MSYS2'
       - script: |
           sfx.exe -y -o%CD:~0,2%\