Update Go version and clean up SMTP test suite

The Go version has been updated to 1.22 in the .golangci.toml file for compatibility reasons. Additionally, unnecessary white space has been removed from the smtp/smtp_test.go file to maximize code efficiency and readability.

.golangci.toml

@@ -3,9 +3,9 @@
 ## SPDX-License-Identifier: MIT
 
 [run]
-go = "1.20"
+go = "1.22"
 tests = true
 
 [linters]
 enable = ["stylecheck", "whitespace", "containedctx", "contextcheck", "decorder",
-    "errname", "errorlint", "gofmt", "gofumpt"]
+    "errname", "errorlint", "gofmt", "gofumpt"]

smtp/smtp_test.go

@@ -1088,7 +1088,6 @@ Subject: SendMail test
 
 SendMail is working for me.
 `, "\n", "\r\n", -1)))
-
 	if err != nil {
 		t.Errorf("%v", err)
 	}