ci: disable e2e-attestationconfigapi on PRs (#2937)

This workflow touches shared state by deleting all objects of a bucket and then
uploading a signed blob of data to that S3 bucket under a fixed name.
It also does so multiple times in a row, while invalidating the cloudfront
cache and checking if the uploaded object exists.
All runs of this workflow share the same bucket.
Since this pipeline runs on any modification of go.mod, it is very prone
to race condition between PRs (or PRs and main).

.github/workflows/e2e-attestationconfigapi.yml

@@ -10,11 +10,6 @@ on:
       - "internal/api/**"
       - ".github/workflows/e2e-attestationconfigapi.yml"
       - "go.mod"
-  pull_request:
-    paths:
-      - "internal/api/**"
-      - ".github/workflows/e2e-attestationconfigapi.yml"
-      - "go.mod"
 
 jobs:
   e2e-api: