[server-pro] test: harden reconfiguring (#28193)

When reconfiguring fails, the config snapshot in the frontend is not
updated. When the next test uses the previous config, it will not
attempt to restore that config again, and instead use the other config.
Reset the config before making changes to ensure all tests get their
desired config, even when reconfiguring fails.

GitOrigin-RevId: 0939e709cf93da820a86fef2599940669138d728

server-ce/test/helpers/config.ts

@@ -53,6 +53,7 @@ export function startWith({
     cy.log(`starting with ${cfg}`)
 
     this.timeout(STARTUP_TIMEOUT)
+    previousConfigFrontend = ''
     const { previousConfigServer } = await reconfigure({
       pro,
       version,
@@ -94,6 +95,7 @@ export async function reloadWith({
   } else if (previousConfigFrontend === cfg) {
     return
   }
+  previousConfigFrontend = ''
   const { previousConfigServer } = await reconfigure({
     pro,
     version,