MinGW no longer provides a 32-bit METIS package

Change-Id: I63b6efd29589b68cf4d16b1ef41c85b3ee437063

.github/workflows/windows.yml

diff --git a/.github/workflows/windows.yml b/.github/workflows/windows.yml
index ee62549..be70f89 100644
--- a/.github/workflows/windows.yml
+++ b/.github/workflows/windows.yml
@@ -37,7 +37,7 @@
           mingw-w64-${{matrix.env}}-gcc
           mingw-w64-${{matrix.env}}-gflags
           mingw-w64-${{matrix.env}}-glog
-          mingw-w64-${{matrix.env}}-metis
+          ${{matrix.sys == 'mingw64' && format('mingw-w64-{0}-metis', matrix.env) || ''}}
           mingw-w64-${{matrix.env}}-ninja
           mingw-w64-${{matrix.env}}-suitesparse