Remove MinGW 32-bit CI (#434)

* CI: Enable automatic Mirror Updates for MSYS2 and bump libobjc2 rt version

* Remove MinGW 32-bit CI and pin runtime version at 2.0

.github/workflows/main.yml

@@ -181,14 +181,6 @@ jobs:
       fail-fast: false
       matrix:
         include:
-          - name: Windows x86 MinGW GCC
-            allow-test-failures: true
-            arch: i686
-            msystem: MINGW32
-            library-combo: gnu-gnu-gnu
-            CC: gcc
-            CXX: g++
-
           - name: Windows x64 MinGW GCC
             arch: x86_64
             msystem: MINGW64
@@ -283,6 +275,7 @@ jobs:
         if: env.CC == 'gcc'
         with:
           msystem: ${{ matrix.msystem }}
+          update: true
           install: >
             mingw-w64-${{matrix.arch}}-gcc-objc