texinfo: fix emission of @footnote directives.

Right now, labels are emitted as part of a @footnote directive.
That results in e.g.

Note1: (@footnote{@w{(1)}
Future versions of GCC may zero-extend...
})

which is incorrect and should be rather:

Note1: (@footnote{Future versions of GCC may zero-extend...})

sphinx/writers/texinfo.py

@@ -761,10 +761,12 @@ def visit_title_reference(self, node: Element) -> None:
     # -- Blocks
 
     def visit_paragraph(self, node: Element) -> None:
-        self.body.append('\n')
+        if not self.in_footnote:
+            self.body.append('\n')
 
     def depart_paragraph(self, node: Element) -> None:
-        self.body.append('\n')
+        if not self.in_footnote:
+            self.body.append('\n')
 
     def visit_block_quote(self, node: Element) -> None:
         self.body.append('\n@quotation\n')
@@ -1223,7 +1225,10 @@ def depart_sidebar(self, node: Element) -> None:
         self.depart_topic(node)
 
     def visit_label(self, node: Element) -> None:
-        self.body.append('@w{(')
+        if self.in_footnote:
+            raise nodes.SkipNode
+        else:
+            self.body.append('@w{(')
 
     def depart_label(self, node: Element) -> None:
         self.body.append(')} ')

tests/test_build_texinfo.py

@@ -112,3 +112,11 @@ def test_texinfo_escape_id(app, status, warning):
     assert translator.escape_id('Hello(world)') == 'Hello world'
     assert translator.escape_id('Hello world.') == 'Hello world'
     assert translator.escape_id('.') == '.'
+
+@pytest.mark.sphinx('texinfo', testroot='footnotes')
+def test_texinfo_footnote(app, status, warning):
+    app.builder.build_all()
+
+    output = (app.outdir / 'python.texi').read_text()
+    assert '@footnote{@w{' not in output
+    assert 'First footnote: @footnote{First}' in output