Edit tests in unit-testing.rst to fix error

[TrueGit]

Q	A
Doc fix?	yes
New docs?	no
Applies to	2.7
Fixed tickets	NA?

In symfony-docs/create_framework/unit-testing.rst, in the
tutorial's "FrameworkTest" class, make following changes to
protected method named "getFrameworkForException" and to test
method named "testControllerResponse":
(i) add mock RequestContext, and
(ii) add to mock URLMatcherInterface the expectation that its
"getContext" method will be called and will return the mock
RequestContext.

Reason: Prior to these changes, running phpunit while following the
unit-testing.rst tutorial causes php error with message:
"Fatal error: Call to a member function fromRequest() on null in
[path/to/]example.com/src/Simplex/Framework.php on line 24"

The line 24 referred to in the foregoing error message is the first
line of the "handle" method of the tutorial's "Framework" class:
"$this->matcher->getContext()->fromRequest($request);"

[wouterj]

Thanks for submitting this fix! Unfortuantely, 2 days before you submitted this PR, someone already submitted a fix: #5488

As that fixed is now merged, I'm going to close this one. Thanks again! 🎄