Merge #6791: backport: bitcoin#27176: docs: GetDataDirNet and GetDataDirBase don't create datadir

c5b325a Merge bitcoin#27176: docs: GetDataDirNet and GetDataDirBase don't create datadir (fanquake)

Pull request description:

  ## Issue being fixed or feature implemented

  Since bitcoin#27073 (backported via #6780), the behaviour of `GetDataDir()` [changed](https://github.com/bitcoin/bitcoin/pull/27073/files#diff-19427b0dd1a791adc728c82e88f267751ba4f1c751e19262cac03cccd2822216L435-L443) to only return the datadir path, but not create it if non-existent. This also changed the behaviour of `GetDataDirNet()` and `GetDataDirBase()` but the docs do not yet reflect that.

  ## How Has This Been Tested?
  N/A

  ## Breaking Changes
  N/A

  ## Checklist:
  - [x] I have performed a self-review of my own code
  - [ ] I have commented my code, particularly in hard-to-understand areas
  - [ ] I have added or updated relevant unit/integration/functional/e2e tests
  - [x] I have made corresponding changes to the documentation
  - [x] I have assigned this pull request to a milestone _(for repository code-owners and collaborators only)_

ACKs for top commit:
  UdjinM6:
    utACK c5b325a
  PastaPastaPasta:
    utACK c5b325a

Tree-SHA512: ff3fa0daea16ddc2d4140e65b7a02926fa2be9adebd6f756868ca985c49a9963950ba1ced1117b3ca289cdda6c7d44e72f51158ced1d3abb5e2f965b81f00896

Author: PastaPastaPasta

src/util/system.h

@@ -307,15 +307,13 @@ class ArgsManager
      * Get data directory path
      *
      * @return Absolute path on success, otherwise an empty path when a non-directory path would be returned
-     * @post Returned directory path is created unless it is empty
      */
     fs::path GetDataDirBase() const { return GetDataDir(false); }
 
     /**
      * Get data directory path with appended network identifier
      *
      * @return Absolute path on success, otherwise an empty path when a non-directory path would be returned
-     * @post Returned directory path is created unless it is empty
      */
     fs::path GetDataDirNet() const { return GetDataDir(true); }