fix: update test fixtures for userId: string after ID->UID merge

Execution.spec.ts, processProgram.spec.ts and code.spec.ts didn't
exist when issue-361 (ID -> UID) branched, so they were written
against the old userId: number shape. Update them to match the
merged-in string-based uid now that main has been merged in.

api/src/controllers/internal/spec/Execution.spec.ts

@@ -8,7 +8,7 @@ import { RunTimeType } from '../../../utils'
 
 const preProgramVariables: PreProgramVars = {
   username: 'testUser',
-  userId: 1,
+  userId: '1',
   displayName: 'Test User',
   serverUrl: 'http://localhost:5000',
   httpHeaders: []