Downgrade go version requirement to 1.19

Previously, we had upgraded this library to be compatible with a
number of features introduced in go 1.20. Our compatibility with the
multi-cause errors does not depend on those features being available
in the stdlib so the requirement in go.mod is being downgraded to
1.19.

This removes the need for an older compatibility branch released as
version 1.10.1 of this library.

Go 1.20 features are only necessary to run tests. GitHub actions are
adjusted to additionally test for a successful build on 1.19.

.github/workflows/ci.yaml

@@ -7,7 +7,24 @@ on:
     branches: [ master ]
 
 jobs:
+  build:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        go:
+          - "1.18"
+          - "1.19"
+          - "1.20"
+    steps:
+      - uses: actions/checkout@v3
+
+      - name: Set up Go (${{ matrix.go }}
+        uses: actions/setup-go@v4
+        with:
+          go-version: ${{ matrix.go }}
 
+      - name: Build (${{ matrix.go }})
+        run: go build ./...
   build-and-test:
     runs-on: ubuntu-latest
     strategy:

go.mod

@@ -1,6 +1,6 @@
 module github.com/cockroachdb/errors
 
-go 1.20
+go 1.19
 
 require (
 	github.com/cockroachdb/datadriven v1.0.2