Use t.Setenv in endtoend tests

t.Setenv restores the previous value when the test exits, which avoids
leaking SQLC_DUMMY_VALUE and the per-example VET_TEST_* URIs into other
tests in the same process.

https://claude.ai/code/session_01RCzB2JR5Y5ScFDUmwcxGVZ

Author: claude

internal/endtoend/endtoend_test.go

@@ -201,7 +201,7 @@ type textContext struct {
 func TestReplay(t *testing.T) {
 	// Ensure that this environment variable is always set to true when running
 	// end-to-end tests
-	os.Setenv("SQLC_DUMMY_VALUE", "true")
+	t.Setenv("SQLC_DUMMY_VALUE", "true")
 
 	// t.Parallel()
 	ctx := context.Background()

internal/endtoend/vet_test.go

@@ -60,11 +60,11 @@ func TestExamplesVet(t *testing.T) {
 				}
 				if s, found := findSchema(t, filepath.Join(path, "mysql")); found {
 					uri := local.MySQL(t, []string{s})
-					os.Setenv(fmt.Sprintf("VET_TEST_EXAMPLES_MYSQL_%s", strings.ToUpper(tc)), uri)
+					t.Setenv(fmt.Sprintf("VET_TEST_EXAMPLES_MYSQL_%s", strings.ToUpper(tc)), uri)
 				}
 				if s, found := findSchema(t, filepath.Join(path, "postgresql")); found {
 					uri := local.PostgreSQL(t, []string{s})
-					os.Setenv(fmt.Sprintf("VET_TEST_EXAMPLES_POSTGRES_%s", strings.ToUpper(tc)), uri)
+					t.Setenv(fmt.Sprintf("VET_TEST_EXAMPLES_POSTGRES_%s", strings.ToUpper(tc)), uri)
 				}
 			}