fix(reporter): add JUnit metadata to GitLab reporter output

[leno23]

Summary

• Adds tests, failures, and errors attributes to <testsuites> and <testsuite> in the GitLab JUnit reporter
• Sets name="SwiftLint" on <testsuite> for clearer CI ingestion (e.g. Bitbucket)

Related to #6161 (JUnit reporter metadata; GitLab reporter was missing the same attributes).

Test plan

• Updated CannedGitLabJUnitReporterOutput.xml fixture
• CI ReporterTests.testGitLabJUnitReporter passes

Made with Cursor

[SwiftLintBot]

	19 Messages
📖	Building this branch resulted in the same binary size as when built on main.
📖	Linting Aerial with this PR took 0.81 s vs 0.81 s on main (0% slower).
📖	Linting Alamofire with this PR took 1.11 s vs 1.09 s on main (1% slower).
📖	Linting Brave with this PR took 7.4 s vs 7.45 s on main (0% faster).
📖	Linting DuckDuckGo with this PR took 29.9 s vs 29.94 s on main (0% faster).
📖	Linting Firefox with this PR took 12.72 s vs 12.74 s on main (0% faster).
📖	Linting Kickstarter with this PR took 8.65 s vs 8.66 s on main (0% faster).
📖	Linting Moya with this PR took 0.48 s vs 0.45 s on main (6% slower).
📖	Linting NetNewsWire with this PR took 2.94 s vs 2.93 s on main (0% slower).
📖	Linting Nimble with this PR took 0.72 s vs 0.69 s on main (4% slower).
📖	Linting PocketCasts with this PR took 8.27 s vs 8.19 s on main (0% slower).
📖	Linting Quick with this PR took 0.44 s vs 0.45 s on main (2% faster).
📖	Linting Realm with this PR took 3.0 s vs 2.98 s on main (0% slower).
📖	Linting Sourcery with this PR took 1.91 s vs 1.93 s on main (1% faster).
📖	Linting Swift with this PR took 4.83 s vs 4.89 s on main (1% faster).
📖	Linting SwiftLintPerformanceTests with this PR took 0.35 s vs 0.35 s on main (0% slower).
📖	Linting VLC with this PR took 1.24 s vs 1.25 s on main (0% faster).
📖	Linting Wire with this PR took 19.33 s vs 19.33 s on main (0% slower).
📖	Linting WordPress with this PR took 13.05 s vs 13.02 s on main (0% slower).

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