Add a test case for imports starting with /.

packages/tailwindcss/src/at-import.test.ts

@@ -120,6 +120,14 @@ test.only.each([
       ${exampleCSS}
     `),
   ],
+  [
+    css`
+      @import url('/example.css');
+    `,
+    optimizeCss(css`
+      ${exampleCSS}
+    `),
+  ],
   [
     css`
       @import url(example.css);
@@ -136,6 +144,14 @@ test.only.each([
       ${exampleCSS}
     `),
   ],
+  [
+    css`
+      @import url(/example.css);
+    `,
+    optimizeCss(css`
+      ${exampleCSS}
+    `),
+  ],
 
   // handles case-insensitive `@import` directive
   [