Fix MATLAB Test Discovery Logic

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This nanoscopic PR fixes #2385 by changing 1 letter.

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And now CI does indeed show that all 17 tests are running:

 *** [1/17] Running matlab/Slice/escape tests ***
...

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Looks like the proxy test is broken.
This was one of the tests which was previously being ignored, so who knows how long it's been broken for...

*** [14/17] Running matlab/Ice/proxy tests ***
...
testing opaque endpoints... Error using Ice.ObjectPrx/ice_ping (line 185)
::Ice::ConnectTimeoutException

Error in AllTests.allTests (line 818)
                p1.ice_encodingVersion(Ice.EncodingVersion(1, 0)).ice_ping();

Error in Client (line 15)
    myClass = AllTests.allTests(helper);

Error in runTest (line 28)
        Client(varargin);