Add tests for old Go versions

Test old verions all the way back to 1.13.

Signed-off-by: SuperQ <superq@gmail.com>

.github/workflows/main.yml

@@ -17,3 +17,15 @@ jobs:
       - run: ./.ci.gofmt.sh
       - run: ./.ci.govet.sh
       - run: go test -v -race ./...
+  test:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        go_version: ["1.13", "1.14", "1.15", "1.16", "1.17", "1.18", "1.19", "1.20"]
+    steps:
+      - uses: actions/checkout@v3
+      - name: Setup Go
+        uses: actions/setup-go@v3.2.0
+        with:
+          go-version: ${{ matrix.go_version }}
+      - run: go test -v -race ./...

go.mod

@@ -1,6 +1,6 @@
 module github.com/stretchr/testify
 
-go 1.20
+go 1.13
 
 require (
 	github.com/davecgh/go-spew v1.1.1