[Github][CI] Enable New Premerge on PRs (#127894)

This patch gets rid of the file restriction for running the new premerge
Github workflow on PRs. This will cause the jobs to be run on all the
PRs. Currently the jobs will succeed regardless of build/test failure
results. This will let us test the new infra hopefully without too much
disruption before eventually letting jobs fail when builds/tests fail
and deprecating the existing premerge system.

This is part of the launch plan as outlined in

https://discourse.llvm.org/t/googles-plan-for-the-llvm-presubmit-infrastructure/78940.

Author: boomanaiden154

.github/workflows/premerge.yaml

@@ -14,8 +14,6 @@ on:
       # do this is that it allows us to take advantage of concurrency groups
       # to cancel in progress CI jobs whenever the PR is closed.
       - closed
-    paths:
-      - .github/workflows/premerge.yaml
   push:
     branches:
       - 'main'