Fix invalid <clear /> element in nuget.config example - #45908

Why:

Closes:

No existing issue — found by parsing every fenced xml block in content/.

"Remove access to public registries" writes the NuGet clear element as < clear />, with a space between the angle bracket and the tag name. XML element names cannot begin with whitespace, so:

• The xml example does not parse as XML.
• NuGet rejects the resulting nuget.config, which is the opposite of what the article is instructing readers to do.

This is a typo rather than a convention: the correct spelling <clear /> is already used twice in Working with the NuGet registry, and < clear /> appears nowhere else in content/.

What's being changed (if available, include any code snippets, screenshots, or gifs):

Removed the stray space in all three occurrences — once in the xml code block, and twice in the prose that describes it (the prose is wrong in the same way, so fixing only the code block would leave the article inconsistent with itself).

After the change the block parses, and the packageSources section resolves as intended:

root = configuration
  child: clear {}
  child: add {'key': 'example-nuget', 'value': 'https://private_registry_url/nuget/example-nuget/index.json'}

Note: this touches the same article as #45907, but a different section and non-overlapping lines, so the two can merge in either order. Happy to combine them if you'd rather review one PR.

Check off the following:

• A subject matter expert (SME) has reviewed the technical accuracy of the content in this PR. In most cases, the author can be the SME. Open source contributions may require an SME review from GitHub staff.
• The changes in this PR meet the docs fundamentals that are required for all content.
• All CI checks are passing and the changes look good in the review environment.