chore: update function pointer signatures with correct args for C23

[nuclearpidgeon]

see: https://gcc.gnu.org/gcc-15/porting_to.html#c23-fn-decls-without-parameters

Fixes another GCC15 build error that's similar to #10471:

Building C object src/proxy/go/CMakeFiles/flb-plugin-proxy-go.dir/go.c.o
/home/stewart/Projects/OSS/fluentbit-4/src/proxy/go/go.c: In function ‘proxy_go_output_init’:
/home/stewart/Projects/OSS/fluentbit-4/src/proxy/go/go.c:110:11: error: too many arguments to function ‘plugin->cb_init’; expected 0, have 1
  110 |     ret = plugin->cb_init(plugin);
      |           ^~~~~~          ~~~~~~
In file included from /home/stewart/Projects/OSS/fluentbit-4/src/proxy/go/go.c:25:
/home/stewart/Projects/OSS/fluentbit-4/src/proxy/go/./go.h:32:11: note: declared here
   32 |     int (*cb_init)();
      |           ^~~~~~~
/home/stewart/Projects/OSS/fluentbit-4/src/proxy/go/go.c: In function ‘proxy_go_input_init’:
/home/stewart/Projects/OSS/fluentbit-4/src/proxy/go/go.c:224:11: error: too many arguments to function ‘plugin->cb_init’; expected 0, have 1
  224 |     ret = plugin->cb_init(plugin);
      |           ^~~~~~          ~~~~~~
/home/stewart/Projects/OSS/fluentbit-4/src/proxy/go/./go.h:45:11: note: declared here
   45 |     int (*cb_init)();
      |           ^~~~~~~
/home/stewart/Projects/OSS/fluentbit-4/src/proxy/go/go.c: In function ‘proxy_go_custom_init’:
/home/stewart/Projects/OSS/fluentbit-4/src/proxy/go/go.c:340:11: error: too many arguments to function ‘plugin->cb_init’; expected 0, have 1
  340 |     ret = plugin->cb_init(plugin);
      |           ^~~~~~          ~~~~~~
/home/stewart/Projects/OSS/fluentbit-4/src/proxy/go/./go.h:57:11: note: declared here
   57 |     int (*cb_init)();
      |           ^~~~~~~

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Fluent Bit is licensed under Apache 2.0, by submitting this pull request I understand that this code will be released under the terms of that license.

[cosmo0920]

Fixes another GCC15 build error that's similar to #10471:

This can be tested with archlinux or other cutting-edge package provided distributions?

[cosmo0920]

Ah, could you split two of the PRs? This is because this PS includes two different changes of modules. So, one is for plugin interface, the other is for in_docker plugin.