refactor(tools): extract function for basicEnvVars docs

As we'll be adding more functionality into this file, and extracting the
function helps keep it clearer what's being done in the function scope.

Author: jamietanna

tools/docs/env-vars.ts

@@ -2,15 +2,21 @@ import { basicEnvVars } from '../../lib/util/exec/env.ts';
 import { readFile, updateFile } from '../utils/index.ts';
 import { replaceContent } from './utils.ts';
 
-export async function generateEnvVars(dist: string): Promise<void> {
+function basicEnvVarsToMarkdown(): string {
   const list = [...basicEnvVars]
     // case-insensitive sort
     .sort((a, b) => a.localeCompare(b, undefined, { sensitivity: 'base' }))
     .map((v) => ` - \`${v}\``)
     .join('\n');
-  const txt = `${list}\n\n`;
+  return `${list}\n\n`;
+}
 
+export async function generateEnvVars(dist: string): Promise<void> {
   let content = await readFile('docs/usage/environment-variable-handling.md');
-  content = replaceContent(content, txt, '<!-- Autogenerate basicEnvVars -->');
+  content = replaceContent(
+    content,
+    basicEnvVarsToMarkdown(),
+    '<!-- Autogenerate basicEnvVars -->',
+  );
   await updateFile(`${dist}/environment-variable-handling.md`, content);
 }