[2.2.x] Changed example git clone URLs to use HTTPS.

Backport of 3c6a4fdb6d from master

docs/internals/contributing/writing-code/unit-tests.txt

@@ -28,7 +28,7 @@ how to do that, read our :doc:`contributing tutorial </intro/contributing>`.
 
 Next, clone your fork, install some requirements, and run the tests::
 
-   $ git clone git@github.com:YourGitHubName/django.git django-repo
+   $ git clone https://github.com/YourGitHubName/django.git django-repo
    $ cd django-repo/tests
    $ pip install -e ..
    $ pip install -r requirements/py3.txt

docs/internals/contributing/writing-code/working-with-git.txt

@@ -45,7 +45,7 @@ When you have created your GitHub account, with the nick "GitHub_nick", and
 `forked Django's repository <https://github.com/django/django/fork>`__,
 create a local copy of your fork::
 
-    git clone git@github.com:GitHub_nick/django.git
+    git clone https://github.com/GitHub_nick/django.git
 
 This will create a new directory "django", containing a clone of your GitHub
 repository. The rest of the git commands on this page need to be run within the

docs/intro/contributing.txt

@@ -113,7 +113,7 @@ Download the Django source code repository using the following command:
 
 .. console::
 
-    $ git clone git@github.com:YourGitHubName/django.git
+    $ git clone https://github.com/YourGitHubName/django.git
 
 .. admonition:: Low bandwidth connection?