Log Message:
libical: update to 3.0.18.

Version 3.0.18 (31 March 2024):
----------------------------
 * Requires CMake v3.5.0 or higher
 * Escape ^ (U+005E) character in parameter values according to RFC 6868
 * New CMake option LIBICAL_BUILD_EXAMPLES to disable building the examples
 * Should be able to use the project as a submodule
 * Built-in timezones updated to tzdata2024a