Fixes https://github.com/libgeos/geos/issues/1084

Resolves https://github.com/libgeos/geos/issues/1073

* Fix overlay op regression with mixed GeometryCollection on 3.9 branch
* Test overlay op with mixed GeometryCollection

Closes #990, References #743

The change was accidentally introduced via commit c4aebbbc
Closes GH-925 in 3.9 branch

In addition to [1]. Otherwise geos fails to build with:
"geos-3.11.1/include/geos/shape/fractal/HilbertEncoder.h:40:28: error: expected ')' before 'p_level'
   40 |     HilbertEncoder(uint32_t p_level, geom::Envelope& extent);
      |                   ~        ^~~~~~~~
      |                            )
/var/tmp/paludis/build/sci-libs-geos-3.11.1/work/geos-3.11.1/include/geos/shape/fractal/HilbertEncoder.h:41:5: error: 'uint32_t' does not name a type
   41 |     uint32_t encode(const geom::Envelope* env);
      |     ^~~~~~~~"

[1] 0e8d4368

Fixes https://github.com/libgeos/geos/issues/821

Fixes https://github.com/libgeos/geos/issues/830