just hardcode bash, maybe that'll work

ci/build.sh

@@ -44,7 +44,7 @@ fi
 if [ "$OS" = "win" ]; then
   VS_WHERE="C:/Program Files (x86)/Microsoft Visual Studio/Installer/vswhere.exe"
   
-  eval "$($(cygpath "$COMSPEC") /c$(cygpath -w "$ROOT/ci/vcvars_export.bat") "$(cygpath -w "$SHELL")")"
+  eval "$($(cygpath "$COMSPEC") /c$(cygpath -w "$ROOT/ci/vcvars_export.bat") bash)"
   
   MSBUILD_EXE=$("$VS_WHERE" -latest -requires Microsoft.Component.MSBuild -find "MSBuild\**\Bin\MSBuild.exe")
   echo $MSBUILD_EXE