Use hyphenated cmdline options in docs (#11490)

Fix #11091

doc/en/deprecations.rst

@@ -645,7 +645,7 @@ By using ``legacy`` you will keep using the legacy/xunit1 format when upgrading
 pytest 6.0, where the default format will be ``xunit2``.
 
 In order to let users know about the transition, pytest will issue a warning in case
-the ``--junitxml`` option is given in the command line but ``junit_family`` is not explicitly
+the ``--junit-xml`` option is given in the command line but ``junit_family`` is not explicitly
 configured in ``pytest.ini``.
 
 Services known to support the ``xunit2`` format:

doc/en/example/markers.rst

@@ -136,7 +136,7 @@ Or select multiple nodes:
 
     Node IDs for failing tests are displayed in the test summary info
     when running pytest with the ``-rf`` option.  You can also
-    construct Node IDs from the output of ``pytest --collectonly``.
+    construct Node IDs from the output of ``pytest --collect-only``.
 
 Using ``-k expr`` to select tests based on their name
 -------------------------------------------------------

doc/en/example/simple.rst

@@ -1090,4 +1090,4 @@ application with standard ``pytest`` command-line options:
 
 .. code-block:: bash
 
-    ./app_main --pytest --verbose --tb=long --junitxml=results.xml test-suite/
+    ./app_main --pytest --verbose --tb=long --junit=xml=results.xml test-suite/

doc/en/how-to/output.rst

@@ -478,7 +478,7 @@ integration servers, use this invocation:
 
 .. code-block:: bash
 
-    pytest --junitxml=path
+    pytest --junit-xml=path
 
 to create an XML file at ``path``.