docs: fixed missing brackets in attachments.md

[Jaskowicz1]

This PR is similar to #838, fixing a missing bracket in attachments.md.

• My pull request is made against the dev branch.
• I have ensured that the changed library can be built on your target system. I did not introduce any platform-specific code.
• I have ensured that all methods and functions are fully documented using doxygen style comments.
• I tested my commits, by adding a test case to the unit tests if needed
• I have ensured that I did not break any existing API calls.
• My code follows the coding style guide (if you are not sure, match the code style of existing files including indent style etc).
• I have not built my pull request using AI, a static analysis tool or similar without any human oversight. Where I have generated this pull request using a tool, I have justified why this is needed.

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[Mishura4]

Examples 1 and 3 still don't build :

[18:00:41] (miuna):~/dev/build/DPP/g++11> g++-11 attachments1.cpp -Llibrary/ -ldpp -I../src/include/ -std=c++17
attachments1.cpp: In lambda function:
attachments1.cpp:13:36: error: ‘const struct dpp::slashcommand_t’ has no member named ‘msg’
   13 |             dpp::message msg(event.msg.channel_id, "Hey there, I've got a new file!");
      |                                    ^~~

[18:06:37] (miuna):~/dev/build/DPP/g++11> g++-11 attachments3.cpp -Llibrary/ -ldpp -I../src/include/ -std=c++17
attachments3.cpp: In lambda function:
attachments3.cpp:14:36: error: ‘const struct dpp::slashcommand_t’ has no member named ‘msg’
   14 |             dpp::message msg(event.msg.channel_id, "");
      |                                    ^~~

[braindigitalis]

Examples 1 and 3 still don't build :

[18:00:41] (miuna):~/dev/build/DPP/g++11> g++-11 attachments1.cpp -Llibrary/ -ldpp -I../src/include/ -std=c++17
attachments1.cpp: In lambda function:
attachments1.cpp:13:36: error: ‘const struct dpp::slashcommand_t’ has no member named ‘msg’
   13 |             dpp::message msg(event.msg.channel_id, "Hey there, I've got a new file!");
      |                                    ^~~

[18:06:37] (miuna):~/dev/build/DPP/g++11> g++-11 attachments3.cpp -Llibrary/ -ldpp -I../src/include/ -std=c++17
attachments3.cpp: In lambda function:
attachments3.cpp:14:36: error: ‘const struct dpp::slashcommand_t’ has no member named ‘msg’
   14 |             dpp::message msg(event.msg.channel_id, "");
      |                                    ^~~

good spot, i didnt catch this!

[Jaskowicz1]

Examples 1 and 3 still don't build :

[18:00:41] (miuna):~/dev/build/DPP/g++11> g++-11 attachments1.cpp -Llibrary/ -ldpp -I../src/include/ -std=c++17

attachments1.cpp: In lambda function:

attachments1.cpp:13:36: error: ‘const struct dpp::slashcommand_t’ has no member named ‘msg’

   13 |             dpp::message msg(event.msg.channel_id, "Hey there, I've got a new file!");

      |                                    ^~~

[18:06:37] (miuna):~/dev/build/DPP/g++11> g++-11 attachments3.cpp -Llibrary/ -ldpp -I../src/include/ -std=c++17

attachments3.cpp: In lambda function:

attachments3.cpp:14:36: error: ‘const struct dpp::slashcommand_t’ has no member named ‘msg’

   14 |             dpp::message msg(event.msg.channel_id, "");

      |                                    ^~~

I'll sort that in the morning!

[Jaskowicz1]

Fixed up the issues that Mishura stated.