CI: enforce packages upgrade for Msys2 on Windows

We need to install libgnutls-devel package to build the host tool,
mkeficapsule, and as of now, there seems to be a depencency conflict
in the current msys2 installer;

   :: installing libp11-kit (0.24.1-1) breaks dependency \
	'libp11-kit=0.23.22' required by p11-kit

To resolve this conflict, however, the initial "pacman -Syyuu" in
'tools_only_windows' job is not enough. Another "pacman -Su" will
enforce all the out-of-date packages being upgraded.
(Probably the first "-Syyuu" can be changed to "-Syu".)

See the installation steps in
  https://www.msys2.org/

Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>

.azure-pipelines.yml

@@ -23,6 +23,7 @@ stages:
       - script: |
           sfx.exe -y -o%CD:~0,2%\
           %CD:~0,2%\msys64\usr\bin\bash -lc "pacman --noconfirm -Syyuu"
+          %CD:~0,2%\msys64\usr\bin\bash -lc "pacman --noconfirm -Su"
         displayName: 'Update MSYS2'
       - script: |
           %CD:~0,2%\msys64\usr\bin\bash -lc "pacman --noconfirm --needed -Sy make gcc bison flex diffutils openssl-devel"