GH-41227: [CI][Release][GLib][Conda] Unpin gobject-introspection (#41228)

### Rationale for this change

Upstream problem conda-forge/glib-feedstock#174 has been fixed.

### What changes are included in this PR?

Revert pinning.

### Are these changes tested?

Yes.

### Are there any user-facing changes?

No.
* GitHub Issue: #41227

Authored-by: Sutou Kouhei <[email protected]>
Signed-off-by: Sutou Kouhei <[email protected]>

Author: kou

dev/release/verify-release-candidate.sh

@@ -831,9 +831,7 @@ test_glib() {
   show_header "Build and test C GLib libraries"
 
   # Build and test C GLib
-  # 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_conda glib gobject-introspection meson ninja ruby
   maybe_setup_virtualenv meson
 
   # Install bundler if doesn't exist