How can I automatically resolve Git conflicts when merging multiple branches

Question

Scenario

In a Jenkins pipeline, there is a stage that clones a repository, let's call it "alert-repo," updates a file named "test.yml," and pushes it back to a Git repository on a branch, then raises a PR against the "master" branch.

This Jenkins workflow is triggered multiple times in parallel, and every time it creates a branch from "master," makes changes to "test.yml," and raises a PR back to "master."

My objective is to automatically merge all the changes from these PRs into the "master" branch without encountering conflicts.

Problem

When I merge the first PR back to "master," subsequent PRs often encounter merge conflicts because all of them are modifying the same file, "test.yml."

For example, if I try to merge branch "b" into "master" after merging branch "a," Git detects conflicts.

I'm seeking a solution to automatically resolve these conflicts and incorporate changes from all the branches without manual intervention.

What I've Tried

1. I've attempted to use Git's default merge strategy, but it doesn't consistently achieve the desired results.
2. I've explored the "ours" and "theirs" merge strategies, but they don't fulfill my requirements.
3. Rebase
4. https://github.com/tibdex/auto-update
5. Putting a github workflow with a hack to slove this but does't help much.

Goal

I'm searching for a solution that enables me to automatically merge both branches "a" and "b" into "master" while retaining as many changes as possible without requiring manual intervention. Is this achievable with Git, and if so, how can I accomplish it?

Welcome to other solutions as well.

Exact User-case

I am implementing alerting using "elasta-alert" and I have a microservices architecture(200+ apps). I want to give developers the power to add their own alerts in their application Helm values file. Then, in the CI stage, I want to compile all the repository files into a Helm values file for "elasta-alert" and apply it. However, if two CI jobs trigger in parallel, clone the elasta-alert helm chart master branch, and raise PRs updating the same file, merging any PR leads to merge conflicts with other PRs.