[ci] Update to msys2/setup-msys2@v2

This update introduces better error handling and package caching by default.
diff --git a/.github/workflows/msys2-ci.yml b/.github/workflows/msys2-ci.yml
index da16ff3..ea4f15f 100644
--- a/.github/workflows/msys2-ci.yml
+++ b/.github/workflows/msys2-ci.yml
@@ -22,7 +22,7 @@
         shell: msys2 {0}
     steps:
       - uses: actions/checkout@v2
-      - uses: msys2/setup-msys2@v1
+      - uses: msys2/setup-msys2@v2
         with:
           msystem: ${{ matrix.MSYSTEM }}
           update: true