Doc: Fix IPAC23 DOI (#454)

Changed since preprint.

docs/source/acknowledge_us.rst

@@ -44,9 +44,8 @@ Further ImpactX References
 
 - Sandberg R T, Lehe R, Mitchell C E, Garten M, Qiang J, Vay J-L and Huebl A.
   **Hybrid Beamline Element ML-Training for Surrogates in the ImpactX Beam-Dynamics Code**.
-  14th International Particle Accelerator Conference (IPAC'23), WEPA101, *in print*, 2023.
-  `preprint <https://www.ipac23.org/preproc/pdf/WEPA101.pdf>`__,
-  `DOI:10.18429/JACoW-IPAC-23-WEPA101 <https://doi.org/10.18429/JACoW-IPAC-23-WEPA101>`__
+  14th International Particle Accelerator Conference (IPAC'23), WEPA101, 2023.
+  `DOI:10.18429/JACoW-IPAC2023-WEPA101 <https://doi.org/10.18429/JACoW-IPAC2023-WEPA101>`__
 
 - Huebl A, Lehe R, Zoni E, Shapoval O, Sandberg R T, Garten M, Formenti A, Jambunathan R, Kumar P, Gott K, Myers A, Zhang W, Almgren A, Mitchell C E, Qiang J, Sinn A, Diederichs S, Thevenet M, Grote D, Fedeli L, Clark T, Zaim N, Vincenti H, Vay JL.
   **From Compact Plasma Particle Sources to Advanced Accelerators with Modeling at Exascale**.