fix(build): pin icu<76 in build deps to match host

The build environment (via qt6-main) was pulling ICU 78 headers while
the host/runtime environment had ICU 75 pinned. The compiled binary
contained icu_78 mangled symbols that fail to resolve against ICU 75
shared libs at runtime. Pin icu>=75,<76 in build deps to match.

package/rattler-build/recipe.yaml

@@ -18,6 +18,7 @@ requirements:
     - cmake
     - compilers>=1.10,<1.11
     - doxygen
+    - icu>=75,<76
     - ninja
     - noqt5
     - python>=3.11,<3.12