fix #3533: properly escape raw XML object

Using string formatting with the raw escaped object lead to string evaluation
"<py._xmlgen.raw object>"
Format the unescaped string first, then use the XML escape method as a last step.

src/_pytest/junitxml.py

@@ -221,12 +221,14 @@ def append_skipped(self, report):
         else:
             filename, lineno, skipreason = report.longrepr
             if skipreason.startswith("Skipped: "):
-                skipreason = bin_xml_escape(skipreason[9:])
+                skipreason = skipreason[9:]
+            details = "%s:%s: %s" % (filename, lineno, skipreason)
+
             self.append(
                 Junit.skipped(
-                    "%s:%s: %s" % (filename, lineno, skipreason),
+                    bin_xml_escape(details),
                     type="pytest.skip",
-                    message=skipreason,
+                    message=bin_xml_escape(skipreason),
                 )
             )
             self.write_captured_output(report)

testing/test_junitxml.py

@@ -1222,3 +1222,19 @@ def test_func():
     assert result.ret == 0
     node = dom.find_first_by_tag("testsuite")
     node.assert_attr(name=expected)
+
+
+def test_escaped_skipreason_issue3533(testdir):
+    testdir.makepyfile(
+        """
+        import pytest
+        @pytest.mark.skip(reason='1 <> 2')
+        def test_skip():
+            pass
+    """
+    )
+    _, dom = runandparse(testdir)
+    node = dom.find_first_by_tag("testcase")
+    snode = node.find_first_by_tag("skipped")
+    assert "1 <> 2" in snode.text
+    snode.assert_attr(message="1 <> 2")