Remove pull_request_target based workflow

.github/workflows/pr-fork.yml

@@ -1,40 +0,0 @@
-name: Pull request
-on:
-  pull_request_target:
-    branches: [master]
-    paths:
-      - .github/workflows/pr-fork.yml
-      - cmd/**
-      - internal/**
-      - .dockerignore
-      - .golangci.yml
-      - Dockerfile
-      - go.mod
-      - go.sum
-
-jobs:
-  test:
-    runs-on: ubuntu-latest
-    steps:
-      - uses: actions/checkout@v2
-      - env:
-          DOCKER_BUILDKIT: "1"
-        run: docker build --target test .
-
-  lint:
-    runs-on: ubuntu-latest
-    steps:
-      - uses: actions/checkout@v2
-      - env:
-          DOCKER_BUILDKIT: "1"
-        run: docker build --target lint .
-
-  docker:
-    runs-on: ubuntu-latest
-    needs: [test, lint]
-    steps:
-      - uses: actions/checkout@v2
-      - name: Docker build
-        env:
-          DOCKER_BUILDKIT: "1"
-        run: docker build .