chore(gitignore): only ignore folders in the top level (#1233)

- [ ] Regenerate this pull request now.

PiperOrigin-RevId: 507603203

Source-Link: https://togithub.com/googleapis/googleapis/commit/a4f2de456480c0a4ed9feeeaa1f8ee620bbef23a

Source-Link: https://togithub.com/googleapis/googleapis-gen/commit/dcf882154e7c710ecf2a1abc77b35c95f9062371
Copy-Tag: eyJwIjoiLmdpdGh1Yi8uT3dsQm90LnlhbWwiLCJoIjoiZGNmODgyMTU0ZTdjNzEwZWNmMmExYWJjNzdiMzVjOTVmOTA2MjM3MSJ9

Author: gcf-owl-bot[bot]

handwritten/bigtable/.gitignore

@@ -1,12 +1,11 @@
 **/*.log
 **/node_modules
-.coverage
-coverage
-.nyc_output
-docs/
-!protos/*
-out/
-build/
+/.coverage
+/coverage
+/.nyc_output
+/docs/
+/out/
+/build/
 system-test/secrets.js
 system-test/*key.json
 *.lock