docs: Update ATLAS 3G tt 2L citation (#1330)

* Update 3G tt 2L CONF note that is superseded by paper
   - c.f. https://inspirehep.net/literature/1844425

docs/bib/use_citations.bib

@@ -75,12 +75,16 @@ @article{Alguero:2020grj
 }
 
 % 2020-08-14
-@Booklet{ATLAS-CONF-2020-046,
-    author         = "{ATLAS Collaboration}",
-    title          = "{Search for new phenomena in events with two opposite-charge leptons, jets and missing transverse momentum in \(pp\) collisions at \(\sqrt{s} = 13\,\text{TeV}\) with the ATLAS detector}",
-    howpublished   = "{ATLAS-CONF-2020-046}",
-    url            = "https://cds.cern.ch/record/2728056",
-    year           = "2020",
+@article{Aad:2021hjy,
+    author = "{ATLAS Collaboration}",
+    title = "{Search for new phenomena in events with two opposite-charge leptons, jets and missing transverse momentum in $pp$ collisions at $\sqrt{s} = 13$ TeV with the ATLAS detector}",
+    eprint = "2102.01444",
+    archivePrefix = "arXiv",
+    primaryClass = "hep-ex",
+    reportNumber = "CERN-EP-2020-243",
+    month = "2",
+    year = "2021",
+    journal = ""
 }
 
 % 2020-06-20