test: add gha ci

Let's see if I remember how to yaml

.github/workflows/test.yaml

@@ -0,0 +1,41 @@
+name: CI Tests
+on:
+  pull_request:
+    paths-ignore:
+      - 'README.md'
+  push:
+    branches:
+      - 'master'
+    paths-ignore:
+      - 'README.md'
+
+permissions:
+  contents: read
+
+jobs:
+  go-fmt-and-vet:
+    runs-on: ubuntu-22.04
+    steps:
+    - uses: actions/checkout@ac593985615ec2ede58e132d2e21d2b1cbd6127c # v3.3.0
+    - uses: actions/setup-go@6edd4406fa81c3da01a34fa6f6343087c207a568 # v3.5.0
+      with:
+        go-version: '1.20'
+        cache: true
+    - run: |
+        files=$(go fmt ./...)
+        if [ -n "$files" ]; then
+          echo "The following file(s) do not conform to go fmt:"
+          echo "$files"
+          exit 1
+        fi
+  go-test:
+    needs: go-fmt-and-vet
+    runs-on: ubuntu-22.04
+    steps:
+    - uses: actions/checkout@ac593985615ec2ede58e132d2e21d2b1cbd6127c # v3.3.0
+    - uses: actions/setup-go@6edd4406fa81c3da01a34fa6f6343087c207a568 # v3.5.0
+      with:
+        go-version: '1.20'
+        cache: true
+    - run: |
+        go test -race ./...

go.mod

@@ -1,3 +1,3 @@
 module github.com/hashicorp/yamux
 
-go 1.15
+go 1.20