This PR fixes an internal source map warning when running tests. To
solve this, we encode the `=` as `\x3d` instead. I'm not 100% sure if
Vitest was hanging on this but it solved the following warning:
```
✓ @tailwindcss/cli src/utils/format-ns.test.ts (21 tests) 3ms
11:43:59 AM [vite] (ssr) Failed to load source map for /Users/robin/github.com/tailwindlabs/tailwindcss/packages/@tailwindcss-node/dist/index.mjs.
Error: An error occurred while trying to read the map file at ${i}
Error: ENOENT: no such file or directory, open '/Users/robin/github.com/tailwindlabs/tailwindcss/packages/@tailwindcss-node/dist/${i}'
at open (node:internal/fs/promises:634:25)
at Object.readFile (node:internal/fs/promises:1238:14)
at extractSourcemapFromFile (file:///Users/robin/github.com/tailwindlabs/tailwindcss/node_modules/.pnpm/vite@7.0.0_@types+node@20.19.1_jiti@2.6.1_lightningcss@1.31.1_patch_hash=tzyxy3asfxcqc7ihroou_7epcep7uhfc7zidzdmxzgvdzwi/node_modules/vite/dist/node/chunks/dep-Bsx9IwL8.js:8349:65)
at loadAndTransform (file:///Users/robin/github.com/tailwindlabs/tailwindcss/node_modules/.pnpm/vite@7.0.0_@types+node@20.19.1_jiti@2.6.1_lightningcss@1.31.1_patch_hash=tzyxy3asfxcqc7ihroou_7epcep7uhfc7zidzdmxzgvdzwi/node_modules/vite/dist/node/chunks/dep-Bsx9IwL8.js:26405:22)
```
## Test plan
1. Existing tests pass
2. Added a failing test to ensure that the source maps are emitted
correctly
6b54dd8630