fixup! Rewrite RTD configuration to use build.jobs rather than build.commands

Add base branch deepening.

Author: zware

.readthedocs.yml

@@ -24,7 +24,14 @@ build:
         if [ "$READTHEDOCS_VERSION_TYPE" = "external" ];
         then
           base_branch=main;
-          git fetch --depth=1 origin $base_branch;
+          git fetch --depth=50 origin $base_branch;
+          for attempt in $(seq 10);
+          do
+            if ! git merge-base HEAD origin/$base_branch;
+            then
+              git fetch --deepen=50 origin $base_branch;
+            fi;
+          done;
           if ! git merge --no-edit origin/$base_branch;
           then
             echo "Unsuccessful merge with '$base_branch' branch, skipping the build";