Revert "Test with Isabelle 2023." - switching back to Isabelle nightly.

This reverts commit e12abadc94.

.woodpecker/build.yml

@@ -1,6 +1,6 @@
 pipeline:
   build:
-    image: git.logicalhacking.com/lh-docker/lh-docker-isabelle/isabelle2023:latest
+    image: git.logicalhacking.com/lh-docker/lh-docker-isabelle/isabelle_nightly:latest
     pull: true
     commands:
       - hg log --limit 2 /root/isabelle
@@ -23,7 +23,7 @@ pipeline:
       - cd ../..
       - ln -s * latest
   archive:
-    image: git.logicalhacking.com/lh-docker/lh-docker-isabelle/isabelle2023:latest
+    image: git.logicalhacking.com/lh-docker/lh-docker-isabelle/isabelle_nightly:latest
     commands:
       - export ARTIFACT_DIR=$CI_WORKSPACE/.artifacts/$CI_REPO/$CI_BRANCH/$CI_BUILD_NUMBER/$LATEX
       - mkdir -p $ARTIFACT_DIR

Isabelle_DOF/scala/dof.scala

@@ -39,10 +39,10 @@ import isabelle._
 object DOF {
   /** parameters **/
 
-  val isabelle_version = "2023"
-  val isabelle_url = "https://isabelle.in.tum.de/website-Isabelle2023" 
+  val isabelle_version = ""
+  val isabelle_url = "https://isabelle.sketis.net/devel/release_snapshot/"
 
-  val afp_version = "afp-2023-09-13"
+  val afp_version = "afp-devel"
 
   // Isabelle/DOF version: "Unreleased" for development, semantic version for releases
   val version = "Unreleased"

README_DEVELOPMENT.md

@@ -5,9 +5,9 @@
 Isabelle/DOF has three major prerequisites:
 
 * **Isabelle:** Isabelle/DOF requires [Isabelle
-  2023](https://isabelle.in.tum.de/website-Isabelle2023/). Please download the
-  Isabelle 2023 distribution for your operating system from the [Isabelle
-  website](https://isabelle.in.tum.de/website-Isabelle2023/).
+  2022](https://isabelle.in.tum.de/website-Isabelle2022/). Please download the
+  Isabelle 2022 distribution for your operating system from the [Isabelle
+  website](https://isabelle.in.tum.de/website-Isabelle2022/).
 * **AFP:** Isabelle/DOF requires several entries from the [Archive of Formal Proofs
   (AFP)](https://www.isa-afp.org/).  
 * **LaTeX:** Isabelle/DOF requires a modern LaTeX installation, i.e., at least