tidy-up: C and CI

- drop redundant casts for `CURL_UNCONST()` pointers (Windows).
- GHA/linux: delete redundant/dupe `-g` C flag in memory sanitizer job.
  Spotted-by: Daniel Stenberg
- examples/http2-upload: drop local macro.
- examples/http2-upload: drop leading underscore from union name.
- examples/http2-upload: drop interim macro.
- tests/server/util: reapply patch lost in a rebase.
- sync `main()` declarations across the codebase.

Closes #22559

tests/server/first.c

@@ -25,7 +25,7 @@
 
 #include <stdio.h>
 
-int main(int argc, const char **argv)
+int main(int argc, const char *argv[])
 {
   entry_func_t entry_func;
   const char *entry_name;

tests/server/util.c

@@ -1097,13 +1097,11 @@ int open_stream_sock(curl_socket_t *psock, uint16_t *pport)
     srvr_sockaddr_union_t localaddr;
     memset(&localaddr, 0, sizeof(localaddr));
 #ifdef USE_IPV6
-    if(socket_domain != AF_INET6)
+    if(socket_domain == AF_INET6)
+      la_size = sizeof(localaddr.sa6);
+    else
 #endif
       la_size = sizeof(localaddr.sa4);
-#ifdef USE_IPV6
-    else
-      la_size = sizeof(localaddr.sa6);
-#endif
     if(getsockname(sock, &localaddr.sa, &la_size) < 0) {
       sockerr = SOCKERRNO;
       logmsg("getsockname() failed with error (%d) %s",