Replace buildkite with GHA (#354)

**What changed?**

Our Buildkite CI config was replaced with GitHub actions


**Why?**

We're trying to deprecate buildkite in general; the server repo has already done so


**Breaking changes**

None.

.github/workflows/ci.yml

@@ -0,0 +1,24 @@
+name: ci
+on:
+  pull_request:
+permissions:
+  contents: read
+jobs:
+  ci:
+    name: ci
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-go@v4
+        with:
+          go-version: '^1.21'
+      - uses: arduino/setup-protoc@v2
+      - run: make ci-build
+      - name: Fail if the repo is dirty
+        run: |
+          if [[ -n $(git status --porcelain) ]]; then
+            echo "Detected uncommitted changes."
+            git status
+            git diff
+            exit 1
+          fi

Makefile

@@ -91,7 +91,7 @@ buf-lint: $(STAMPDIR)/buf-mod-prune
 
 buf-breaking:
 	@printf $(COLOR) "Run buf breaking changes check against master branch..."	
-	@(cd $(PROTO_ROOT) && buf breaking --against '.git#branch=master')
+	@(cd $(PROTO_ROOT) && buf breaking --against 'https://github.com/temporalio/api.git#branch=master')
 
 ##### Clean #####
 clean:

buf.lock

@@ -5,7 +5,9 @@ deps:
     owner: googleapis
     repository: googleapis
     commit: 28151c0d0a1641bf938a7672c500e01d
+    digest: shake256:49215edf8ef57f7863004539deff8834cfb2195113f0b890dd1f67815d9353e28e668019165b9d872395871eeafcbab3ccfdb2b5f11734d3cca95be9e8d139de
   - remote: buf.build
     owner: grpc-ecosystem
     repository: grpc-gateway
     commit: 048ae6ff94ca4476b3225904b1078fad
+    digest: shake256:e5250bf2d999516c02206d757502b902e406f35c099d0e869dc3e4f923f6870fe0805a9974c27df0695462937eae90cd4d9db90bb9a03489412560baa74a87b6