Go: Add test for go/autobuilder/invalid-go-toolchain-version diagnostic

Author: mbg

go/ql/integration-tests/all-platforms/go/diagnostics/invalid-toolchain-version/diagnostics.expected

@@ -0,0 +1,31 @@
+{
+  "location": {
+    "file": "go.mod"
+  },
+  "markdownMessage": "As of Go 1.21, toolchain versions [must use the 1.N.P syntax](https://tip.golang.org/doc/toolchain#version).\n\n`1.21` in `go.mod` does not match this syntax and there is no additional `toolchain` directive, which may cause some `go` commands to fail.",
+  "severity": "warning",
+  "source": {
+    "extractorName": "go",
+    "id": "go/autobuilder/invalid-go-toolchain-version",
+    "name": "`1.21` is not a valid Go toolchain version"
+  },
+  "visibility": {
+    "cliSummaryTable": true,
+    "statusPage": true,
+    "telemetry": true
+  }
+}
+{
+  "markdownMessage": "A single `go.mod` file was found.\n\n`go.mod`",
+  "severity": "note",
+  "source": {
+    "extractorName": "go",
+    "id": "go/autobuilder/single-root-go-mod-found",
+    "name": "A single `go.mod` file was found in the root"
+  },
+  "visibility": {
+    "cliSummaryTable": false,
+    "statusPage": false,
+    "telemetry": true
+  }
+}

go/ql/integration-tests/all-platforms/go/diagnostics/invalid-toolchain-version/src/go.mod

@@ -0,0 +1,3 @@
+go 1.21
+
+module example

go/ql/integration-tests/all-platforms/go/diagnostics/invalid-toolchain-version/src/main.go

@@ -0,0 +1,5 @@
+package main
+
+func main() {
+
+}

go/ql/integration-tests/all-platforms/go/diagnostics/invalid-toolchain-version/test.py

@@ -0,0 +1,19 @@
+import os
+import subprocess
+
+from create_database_utils import *
+from diagnostics_test_utils import *
+
+# Set up a GOPATH relative to this test's root directory;
+# we set os.environ instead of using extra_env because we
+# need it to be set for the call to "go clean -modcache" later
+goPath = os.path.join(os.path.abspath(os.getcwd()), ".go")
+os.environ['GOPATH'] = goPath
+os.environ['LGTM_INDEX_IMPORT_PATH'] = "test"
+run_codeql_database_create([], lang="go", source="src")
+
+check_diagnostics()
+
+# Clean up the temporary GOPATH to prevent Bazel failures next
+# time the tests are run; see https://github.com/golang/go/issues/27161
+subprocess.call(["go", "clean", "-modcache"])