Update pubs.opengroup.org links for POSIX 2024 (and https).

Change-Id: I5ac55398561c3da5b7915a479dbbb709ae98c758
diff --git a/libc/bionic/system.cpp b/libc/bionic/system.cpp
index 93d7497..8349498 100644
--- a/libc/bionic/system.cpp
+++ b/libc/bionic/system.cpp
@@ -38,7 +38,7 @@
 
 int system(const char* command) {
   // "The system() function shall always return non-zero when command is NULL."
-  // http://pubs.opengroup.org/onlinepubs/9699919799/functions/system.html
+  // https://pubs.opengroup.org/onlinepubs/9799919799.2024edition/functions/system.html
   if (command == nullptr) return 1;
 
   ScopedSignalBlocker sigchld_blocker(SIGCHLD);