migrate 'main' tests to GH actions (#8332)

* implement 'main' tests using GH actions

* remove 'main' builds from Circle CI config

* give jobs better names

scripts/mocha2md.js

@@ -0,0 +1,36 @@
+import fs from 'fs'
+
+let data
+let title
+
+try {
+  if (process.argv.length < 4) {
+    throw new Error()
+  }
+  title = process.argv[2]
+  data = JSON.parse(fs.readFileSync(process.argv[3]))
+} catch (e) {
+  process.stdout.write('failed to write summary\n')
+  process.exit(1)
+}
+
+process.stdout.write(`# ${title}\n\n`)
+
+if (data.stats.passes > 0) {
+  process.stdout.write(`✔ ${data.stats.passes} passed\n`)
+}
+if (data.stats.failures > 0) {
+  process.stdout.write(`✖ ${data.stats.failures} failed\n\n`)
+}
+
+if (data.stats.failures > 0) {
+  for (const test of data.tests) {
+    if (test.err && Object.keys(test.err).length > 0) {
+      process.stdout.write(`### ${test.title}\n\n`)
+      process.stdout.write(`${test.fullTitle}\n\n`)
+      process.stdout.write('```\n')
+      process.stdout.write(`${test.err.stack}\n`)
+      process.stdout.write('```\n\n')
+    }
+  }
+}