tidy up [GitHubGist] routes (#8510)

Co-authored-by: repo-ranger[bot] <39074581+repo-ranger[bot]@users.noreply.github.com>

services/github/gist/github-gist-last-commit.tester.js

@@ -0,0 +1,24 @@
+import { createServiceTester } from '../../tester.js'
+export const t = await createServiceTester()
+
+t.create('last commit in gist (ancient)').get('/871064.json').expectBadge({
+  label: 'last commit',
+  message: 'september 2015',
+  color: 'red',
+})
+
+// not checking the color badge, since in August 2022 it is orange but later it will become red
+t.create('last commit in gist (still ancient but slightly less so)')
+  .get('/870071abadfd66a28bf539677332f12b.json')
+  .expectBadge({
+    label: 'last commit',
+    message: 'october 2020',
+  })
+
+t.create('last commit in gist (gist not found)')
+  .get('/55555555555555.json')
+  .expectBadge({
+    label: 'last commit',
+    message: 'gist not found',
+    color: 'red',
+  })