fix: fixed link to non-existent forum with link to actual forum [skip tests] (#4585)

## Context
The pyfluent homepage pointed to a non-existent forum

## Change Summary
The target url was changed and the text for it was changed

## Rationale
discuss.ansys.com is the official place for PyAnsys questions and
discussions

## Impact
Docs only.

---------

Co-authored-by: pyansys-ci-bot <[email protected]>

Author: jgd10

doc/changelog.d/4585.fixed.md

@@ -0,0 +1 @@
+Fixed link to non-existent forum with link to actual forum [skip tests]

doc/source/index.rst

@@ -63,7 +63,7 @@ Need Help?
 
 Visit the community or support resources:
 
-- `PyAnsys community forum <https://forum.pyansys.com>`_
+- `Ansys developer forum <https://discuss.ansys.com>`_
 - `Submit a bug report <https://github.com/ansys/pyfluent/issues>`_
 - `Contact support <https://support.ansys.com>`_