Fix init_go_test hitting GitHub API rate limit in CI

Pin init_go_test to --version v1.29.0, matching how the python and cc
plugin init tests already avoid the GitHub API. Also add GITHUB_TOKEN
support to getLatestRevision() so unauthenticated rate limits (60/hr)
don't break CI when the API is hit for real.

Author: sean-

src/plzinit/plugins.go

@@ -253,6 +253,9 @@ func getLatestRevision(plugin string) (string, error) {
 		return "", err
 	}
 	req.Header.Set("accept", "application/vnd.github.v3+json")
+	if token := os.Getenv("GITHUB_TOKEN"); token != "" {
+		req.Header.Set("Authorization", "token "+token)
+	}
 	client := &http.Client{}
 	resp, err := client.Do(req)
 	if err != nil {

test/plugins/BUILD

@@ -91,7 +91,7 @@ plugin_e2e_test(
         "go.conf": "//third_party/go:toolchain|go\n//third_party/go:std",
     },
     # Need to break hard link here so init_plugin_test's actual .plzconfig doesn't get updated.
-    plz_command = "cp .plzconfig .foo; mv .foo .plzconfig; plz init plugin go && plz query config plugin.go.gotool > go.conf && plz query config plugin.go.stdlib >> go.conf",
+    plz_command = "cp .plzconfig .foo; mv .foo .plzconfig; plz init plugin go --version v1.29.0 && plz query config plugin.go.gotool > go.conf && plz query config plugin.go.stdlib >> go.conf",
 )
 
 # Test that the target is created in plugins/BUILD