tests: rename _test.v files with dup names (temp workaround for highly parallel testing)

vlib/encoding/utf8/encoding_utf8_test.v

@@ -0,0 +1,9 @@
+import encoding.utf8 { validate_str }
+
+fn test_validate_str() {
+	assert validate_str('añçá') == true
+	assert validate_str('\x61\xC3\xB1\xC3\xA7\xC3\xA1') == true
+	assert validate_str('\xC0\xC1') == false
+	assert validate_str('\xF5\xFF') == false
+	assert validate_str('\xE0\xEF') == false
+}