GH-41167: [CI][Release][GLib][Conda] Pin gobject-introspection to 1.7…

…8.1 (#41181)

### Rationale for this change

GObject Introspection is merging into GLib. It's not completed yet.

GLib related `.gir` files are moved to GLib from GObject Introspection since GLib/GObject Introspection 2.80.0. But glib 2.80.0 conda package doesn't support this merge yet:  conda-forge/glib-feedstock#174

### What changes are included in this PR?

Pin gobject-introspection to 1.78.1 for now. 

### Are these changes tested?

Yes.

### Are there any user-facing changes?

No.
* GitHub Issue: #41167

Authored-by: Sutou Kouhei <kou@clear-code.com>
Signed-off-by: Sutou Kouhei <kou@clear-code.com>

dev/release/verify-release-candidate.sh

@@ -831,7 +831,9 @@ test_glib() {
  show_header "Build and test C GLib libraries"
 
  # Build and test C GLib
- maybe_setup_conda glib gobject-introspection meson ninja ruby
+ # We can unpin gobject-introspection after
+ # https://github.com/conda-forge/glib-feedstock/pull/174 is merged.
+ maybe_setup_conda glib gobject-introspection=1.78.1 meson ninja ruby
  maybe_setup_virtualenv meson
 
  # Install bundler if doesn't exist