Adds libgfortran dependency

Adds libgfortran as a dependency to the xtb environment.
This ensures that the xtb package has the necessary Fortran
libraries available during execution.

Author: calvinp0

devtools/xtb_environment.yml

@@ -5,4 +5,4 @@ dependencies:
   - python=3.7
   - xtb=6.3.3
   - pyyaml
-  
+  - libgfortran=14.2.0