Pin rust toolchain (#14817)

* Pin rust toolchain

* Always install targets in build script

* Delete installed toolchains

.github/renovate.json5

@@ -51,6 +51,12 @@
       commitMessagePrefix: "[deps] BRE:",
       addLabels: ["hold"],
     },
+    {
+      // Enable support for Rust toolchain updates.
+      matchManagers: ["custom.regex"],
+      matchDepNames: ["rust"],
+      commitMessageTopic: "Rust",
+    },
     {
       // By default, we send patch updates to the Dependency Dashboard and do not generate a PR.
       // We want to generate PRs for a select number of dependencies to ensure we stay up to date on these.