gh-38981: Fix broken rendering of adjacent code blocks

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a bug seen in, for example: https://doc-release--sagemath.netlify.app/ht
ml/en/reference/structure/sage/structure/category_object#sage.structure.
category_object.CategoryObject.variable_names

Compare with the fixed page: https://doc-pr-38981--sagemath.netlify.app/
html/en/reference/structure/sage/structure/category_object#sage.structur
e.category_object.CategoryObject.variable_names

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- [ ] I have updated the documentation and checked the documentation
preview.

### ⌛ Dependencies

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URL: #38981
Reported by: Kwankyu Lee
Reviewer(s): Frédéric Chapoton

build/pkgs/configure/checksums.ini

@@ -1,3 +1,3 @@
 tarball=configure-VERSION.tar.gz
-sha1=87648980fa41bbd38f9bf45beb7bcdb90e12d613
-sha256=cb5129b2e60af70968a6d8de8937b0f9365a2146762bf34a09b4ad7a88c56b8b
+sha1=75d6eb488fd370ea17699188dabf78afa295d6d9
+sha256=679c7a5c352eeac458ee6574326208df1bc0b30be5c803b952e19a9d2a8b7d32

build/pkgs/configure/package-version.txt

@@ -1 +1 @@
-d9c38a7c581e6ed54fbe420122b8bba488b16074
+659705e89638fae6821783730c357bf292ebed6e

src/sage_docbuild/conf.py

@@ -954,16 +954,17 @@ class SagecodeTransform(SphinxTransform):
 
     def apply(self):
         if self.app.builder.tags.has('html') or self.app.builder.tags.has('inventory'):
-            for node in self.document.findall(nodes.literal_block):
+            for node in list(self.document.findall(nodes.literal_block)):
                 if node.get('language') is None and node.astext().startswith('sage:'):
                     from docutils.nodes import container as Container, label as Label, literal_block as LiteralBlock, Text
                     from sphinx_inline_tabs._impl import TabContainer
                     parent = node.parent
                     index = parent.index(node)
                     prev_node = node.previous_sibling()
-                    if isinstance(node.previous_sibling(), TabContainer):
+                    if isinstance(prev_node, TabContainer):
                         # Make sure not to merge inline tabs for adjacent literal blocks
-                        parent.insert(index, Text(''))
+                        parent.insert(index, nodes.paragraph())
+                        prev_node = parent[index]
                         index += 1
                     parent.remove(node)
                     # Tab for Sage code