revert test file rename (not found for some reason)

Author: janosh

tests/files/vasp/outputs/vasprun.ediffg=0.xml.gz renamed to tests/files/vasp/outputs/vasprun.ediffg_set_to_0.xml.gz

@@ -76,7 +76,7 @@ def test_vasprun_md(self):
 
     def test_vasprun_ediffg_set_to_0(self):
         # Test for case where EDIFFG is set to 0.
-        vasp_run = Vasprun(f"{VASP_OUT_DIR}/vasprun.ediffg=0.xml.gz")
+        vasp_run = Vasprun(f"{VASP_OUT_DIR}/vasprun.ediffg_set_to_0.xml.gz")
         assert len(vasp_run.ionic_steps) == 3
         assert vasp_run.final_energy == approx(-34.60164204)
         assert vasp_run.converged_ionic