STYLE: Fix XML namespace of natstepfilter file (Visual Studio Debugger)

According to  Learn / Visual Studio / Debugging, section "Customize C++ stepping
behavior independent of Just My Code settings"
(https://learn.microsoft.com/en-us/visualstudio/debugger/just-my-code?view=vs-2022#BKMK_CPP_Customize_stepping_behavior)
the name of the XML namespace specified by the `xmlns` attribute in a
natstepfilter file starts with "http:" (not "https:"). While "https:" might work
in this particular case, it appears preferable to use the officially documented
XML namespace name.

Reverts the change of this particular file from pull request #3428
commit 9cd0f20 "ENH: Use https instead of http
when https works", May 18, 2022.

Utilities/Debugger/default.natstepfilter

@@ -1,6 +1,6 @@
 <?xml version="1.0" encoding="utf-8"?>
 <!-- Copy into C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\Common7\Packages\Debugger\Visualizers\default.natstepfilter -->
-<StepFilter xmlns="https://schemas.microsoft.com/vstudio/debugger/natstepfilter/2010">
+<StepFilter xmlns="http://schemas.microsoft.com/vstudio/debugger/natstepfilter/2010">
   <Function><Name>__security_check_cookie</Name><Action>NoStepInto</Action></Function>
   <Function><Name>__abi_winrt_.*</Name><Action>NoStepInto</Action></Function>
   <Function><Name>_ObjectStublessClient.*</Name><Action>NoStepInto</Action></Function>