Update min node version to 18, add 20 to supported versions & CI (#6447)

* Update min node version to 18, add 20 to supported versions & CI

* Fix broken unit test

* Bump dockefiles to Node 20 as well

Author: joehan

scripts/build/Dockerfile

@@ -1,4 +1,4 @@
-FROM node:18
+FROM node:20
 
 # Install dependencies
 RUN apt-get update && \

scripts/firepit-builder/Dockerfile

@@ -1,4 +1,4 @@
-FROM node:18
+FROM node:20
 
 # Install dependencies
 RUN apt-get update && \

src/test/apiv2.spec.ts

@@ -158,7 +158,7 @@ describe("apiv2", () => {
         method: "GET",
         path: "/path/to/foo",
       });
-      await expect(r).to.eventually.be.rejectedWith(FirebaseError, /Unexpected token.+JSON/);
+      await expect(r).to.eventually.be.rejectedWith(FirebaseError, /Unable to parse JSON/);
       expect(nock.isDone()).to.be.true;
     });