ci: tests were written by someone in PRC timezone

Nothing was working if you were not in this timezone.

The CI was forced in this timezone, but it was uneasy to catch.

Now all tests are launched in the PRC timezone.

We are using TestMain to sort this out.
https://pkg.go.dev/testing#hdr-Main

.github/workflows/test.yml

@@ -2,8 +2,6 @@ name: test
 
 on:
   push
-env:
-  TZ: "PRC"
 jobs:
 
   test:

test.go

@@ -1,6 +1,7 @@
 package carbon
 
 import (
+	"os"
 	"testing"
 )
 
@@ -22,6 +23,18 @@ func (c Carbon) IsSetTestNow() bool {
 	return c.testNow > 0
 }
 
+// TestMain sets up the testing environment for all tests
+// https://pkg.go.dev/testing#hdr-Main
+func TestMain(m *testing.M) {
+	// The whole tests were written for PRC timezone (China).
+	// The codebase of test is too large to be changed.
+	// Without this hack the tests will fail if you use a different timezone than PRC
+	// This will affect the way Go compute the timezone when using time.Local
+	_ = os.Setenv("TZ", "PRC")
+
+	m.Run()
+}
+
 func prepareTest(tb testing.TB) {
 	tb.Helper()