fix(coverage): thresholds to compare files relative to root

[AriPerkkio]

Description

• Fixes Threshold on a Glob Pattern does not show an error message #5545

In following project:

<root>
|
├── package.json
├── vitest.config.ts
├── src
|  └── utils.ts
└── test
   └── utils.test.ts

... users no longer need to define **/src/utils.ts in coverage.thresholds[<glob>]. A simple src/utils.ts works now.

import { defineConfig } from "vitest/config";

export default defineConfig({
  test: {
    coverage: {
      thresholds: {
-       '**/src/utils.ts': {
+       'src/utils.ts': {
          functions: 100,
        },
      },
    },
  },
});

Documentation is already using this pattern:

vitest/docs/config/index.md

Lines 1322 to 1328 in 413ec5e

	// Thresholds for matching glob pattern
	'src/utils/**.ts': {
	statements: 95,
	functions: 90,
	branches: 85,
	lines: 80,
	},

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