fix: evaluate schedules in the cronjob's spec.timeZone (#428)

Schedules were always evaluated in UTC because `schedule.Next` uses the location of `lastScheduleTime`, which the API returns in UTC. A CronJob with `spec.timeZone` set was therefore reported as not running every day. For example, Paidit's `prod/dayclose` runs at `0 7 * * *` Europe/Stockholm: it ran at 05:00Z, but cron-checker expected 07:00Z and alerted every minute from 09:02 local time.

- Convert `since` to the CronJob's `spec.timeZone` before computing the next run. CronJobs without a `timeZone` behave as before.
- An invalid time zone returns an error, the same way an invalid schedule does.
- Embed `time/tzdata`, because the image is `FROM scratch` and has no zoneinfo.
- Tests: an invalid time zone, and a time-zone case that fails without the fix.
- Bumped golang.org/x/net to v0.60.0. govulncheck was already failing on main with five x/net advisories, which blocks the build job.
- Bumped the go toolchain to 1.27.2 for eight stdlib advisories. This is the same change as Renovate #427, which will close once this is merged.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

https://claude.ai/code/session_01C8SW6vsbkrTKjLNatQ8JTg
Reviewed-on: https://gitea.unbound.se/unboundsoftware/cron-checker/pulls/428

main_test.go

@@ -106,6 +106,7 @@ func Test_doCheck(t *testing.T) {
 		slackResponse string
 		wantErr       bool
 		wantOut       []string
+		wantNotOut    []string
 	}{
 		{
 			name: "error getting cronjobs",
@@ -181,6 +182,57 @@ func Test_doCheck(t *testing.T) {
 			},
 			wantErr: true,
 		},
+		{
+			name: "invalid time zone",
+			args: args{
+				client: &brokenClient{
+					batchApi: &batchApi{
+						cronApi: &cronApi{
+							listFn: func(_ context.Context, _ v1.ListOptions) (*cronjobv1.CronJobList, error) {
+								return &cronjobv1.CronJobList{
+									Items: []cronjobv1.CronJob{
+										{
+											Spec: cronjobv1.CronJobSpec{Schedule: "* * * * *", TimeZone: strP("Nowhere/Special")},
+										},
+									},
+								}, nil
+							},
+						},
+					},
+				},
+			},
+			wantErr: true,
+		},
+		{
+			name: "schedule evaluated in cronjob time zone",
+			args: args{
+				client: &brokenClient{
+					batchApi: &batchApi{
+						cronApi: &cronApi{
+							listFn: func(_ context.Context, _ v1.ListOptions) (*cronjobv1.CronJobList, error) {
+								// Ran 6h ago at its daily local time; read as UTC the next run would be 30 minutes ago
+								last := time.Now().Add(-6 * time.Hour).Truncate(time.Minute)
+								local := last.In(time.FixedZone("IST", 5*3600+1800)) // Asia/Kolkata has no DST
+								return &cronjobv1.CronJobList{
+									Items: []cronjobv1.CronJob{
+										{
+											ObjectMeta: v1.ObjectMeta{Name: "some-name", Namespace: "some-ns"},
+											Spec:       cronjobv1.CronJobSpec{Schedule: fmt.Sprintf("%d %d * * *", local.Minute(), local.Hour()), TimeZone: strP("Asia/Kolkata")},
+											Status:     cronjobv1.CronJobStatus{LastScheduleTime: &v1.Time{Time: last}},
+										},
+									},
+								}, nil
+							},
+						},
+					},
+				},
+			},
+			timeout:       100 * time.Millisecond,
+			slackResponse: `{"ok": true}`,
+			wantErr:       false,
+			wantOut:       []string{"Checking some-ns/some-name since"},
+			wantNotOut:    []string{"was not scheduled"},
+		},
 		{
 			name: "only correctly running cronjobs",
 			args: args{
@@ -308,6 +360,11 @@ func Test_doCheck(t *testing.T) {
 			if err := doCheck(tt.args.client, fmt.Sprintf("http://%s", baseURL), ic, 10*time.Millisecond, buff); (err != nil) != tt.wantErr {
 				t.Errorf("doCheck() error = %v, wantErr %v", err, tt.wantErr)
 			}
+			for _, o := range tt.wantNotOut {
+				if strings.Contains(buff.String(), o) {
+					t.Errorf("doCheck() got %s, did not want %s", buff.String(), o)
+				}
+			}
 			if len(tt.wantOut) > 0 {
 				for _, o := range tt.wantOut {
 					if !strings.Contains(buff.String(), o) {
@@ -404,7 +461,7 @@ func (b batchApi) CronJobs(namespace string) batchv1.CronJobInterface {
 }
 
 func (b batchApi) Jobs(namespace string) batchv1.JobInterface {
-	//TODO implement me
+	// TODO implement me
 	panic("implement me")
 }
 
@@ -463,3 +520,7 @@ var _ batchv1.CronJobInterface = &cronApi{}
 func boolP(b bool) *bool {
 	return &b
 }
+
+func strP(s string) *string {
+	return &s
+}