Enable optimizations in cross MSW CI builds

Amazingly, it seems that the latest gcc 12-based MinGW miscompiles
something in TIFF code _without_ optimizations as the SaveTIFF() test
fails when compiled with -O0 but works with -O2, so try enabling the
optimizations for this test.

It also makes more sense to run tests against the production/release
versions of the library anyhow, we only used --disable-optimise to save
on build time, but perhaps this is not as critical any longer.

.github/workflows/ci_msw_cross.yml

@@ -147,7 +147,7 @@ jobs:
 
       - name: Configure
         run: |
-          ./configure --host=${HOST_TRIPLET} --disable-sys-libs --disable-optimise --disable-debug_info $wxCONFIGURE_FLAGS || rc=$?
+          ./configure --host=${HOST_TRIPLET} --disable-sys-libs --disable-debug_info $wxCONFIGURE_FLAGS || rc=$?
 
           if [ -n "$rc" ]; then
             echo '*** Configuring failed, contents of config.log follows: ***'