ci: re-add Go 1.12.x to the build matrix

We still guarantee support for Go 1.12.x. Hence this needs to be part of
the build matrix. My bad having removed this in a previous CL.

Change-Id: I4fc546c5f94b4af3a980253cfd3aca9f1366b08c
Reviewed-on: https://cue-review.googlesource.com/c/cue/+/6180
Reviewed-by: CUE cueckoo <cueckoo@gmail.com>
Reviewed-by: Paul Jolly <paul@myitcv.org.uk>
diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index a8d5047..c25a349 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -50,6 +50,7 @@
     strategy:
       matrix:
         go-version:
+        - 1.12.x
         - 1.13.x
         - 1.14.3
         os:
diff --git a/.github/workflows/test_dispatch.yml b/.github/workflows/test_dispatch.yml
index 37b4424..857ecc1 100644
--- a/.github/workflows/test_dispatch.yml
+++ b/.github/workflows/test_dispatch.yml
@@ -55,6 +55,7 @@
     strategy:
       matrix:
         go-version:
+        - 1.12.x
         - 1.13.x
         - 1.14.3
         os:
diff --git a/internal/ci/workflows.cue b/internal/ci/workflows.cue
index a00547a..35d3d20 100644
--- a/internal/ci/workflows.cue
+++ b/internal/ci/workflows.cue
@@ -36,7 +36,7 @@
 	"fail-fast": false
 	matrix: {
 		// Use a stable version of 1.14.x for go generate
-		"go-version": ["1.13.x", "1.14.3"]
+		"go-version": ["1.12.x", "1.13.x", "1.14.3"]
 		os: ["ubuntu-latest", "macos-latest", "windows-latest"]
 	}
 }