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

docs/internals/CODE_STYLE.md

@@ -104,7 +104,7 @@ if(!x)
 For functions the opening brace should be on a separate line:
 
 ```c
-int main(int argc, char **argv)
+int main(int argc, char *argv[])
 {
   return 1;
 }