Implement fallback to global git config for user name retrieval

[xping-admin]

Enhance user name retrieval by checking the global git configuration if no local configuration is found. This change ensures a more robust method for obtaining user information in various environments.

[Copilot]

Pull request overview

Adds a fallback in EnvironmentDetector so that when the local .git/config does not contain a [user] name, the global git config locations ($HOME/.gitconfig and $XDG_CONFIG_HOME/git/config) are consulted. Also suppresses CA5394 in sample projects.

Changes:

• Refactor ReadGitConfigUserName to first read local repo config, then fall back to $HOME/.gitconfig, then XDG-style $XDG_CONFIG_HOME/git/config, extracting the file-parsing logic into a helper ReadUserNameFromFile.
• Add an xUnit test exercising the global-config fallback path using a temporary HOME directory.
• Suppress CA5394 (insecure randomness) in sample projects with an explanatory comment.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
src/Xping.Sdk.Core/Services/Environment/Internals/EnvironmentDetector.cs	Implements the local → global → XDG fallback chain for git user name.
tests/Xping.Sdk.Core.Tests/Services/Environment/EnvironmentDetectorTests.cs	New test covering global-config fallback when local [user] is absent.
samples/Directory.Build.props	Suppress CA5394 in samples (random for flaky-test simulation).

[codecov]

Codecov Report

❌ Patch coverage is 43.75000% with 9 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...vices/Environment/Internals/EnvironmentDetector.cs	43.75%	6 Missing and 3 partials ⚠️

Files with missing lines	Coverage Δ
...vices/Environment/Internals/EnvironmentDetector.cs	50.37% <43.75%> (+0.90%)	⬆️

... and 1 file with indirect coverage changes

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