Fix formatting of \0 in tests

This follows this PR in rustc:
<rust-lang/rust#95345>

Which breakage was discussed here:
<rust-lang/rust#95732>

Because this landed in 1.61.0, the MSRV has to be updated accordingly.

Cargo.toml

@@ -10,6 +10,7 @@ license = "MIT/Apache-2.0"
 readme = "README.md"
 repository = "https://github.com/RazrFalcon/xmlparser"
 edition = "2018"
+rust-version = "1.61.0"
 
 [features]
 default = ["std"]

tests/integration/cdata.rs

@@ -71,5 +71,5 @@ test!(cdata_09, "<p><![CDATA[bracket ]after]]></p>",
 test!(cdata_err_01, "<p><![CDATA[\0]]></p>",
     Token::ElementStart("", "p", 0..2),
     Token::ElementEnd(ElementEnd::Open, 2..3),
-    Token::Error("invalid CDATA at 1:4 cause a non-XML character '\\u{0}' found at 1:13".to_string())
+    Token::Error("invalid CDATA at 1:4 cause a non-XML character '\\0' found at 1:13".to_string())
 );

tests/integration/elements.rs

@@ -211,7 +211,7 @@ test!(attribute_err_05, "<c a='<'/>",
 
 test!(attribute_err_06, "<c a='\0'/>",
     Token::ElementStart("", "c", 0..2),
-    Token::Error("invalid attribute at 1:3 cause a non-XML character '\\u{0}' found at 1:7".to_string())
+    Token::Error("invalid attribute at 1:3 cause a non-XML character '\\0' found at 1:7".to_string())
 );
 
 test!(attribute_err_07, "<c a='v'b='v'/>",

tests/integration/pi.rs

@@ -119,7 +119,7 @@ test!(declaration_err_12, "<?xml version='1.0'?><?xml version='1.0'?>",
 );
 
 test!(declaration_err_13, "<?target \u{0000}content>",
-    Token::Error("invalid processing instruction at 1:1 cause a non-XML character '\\u{0}' found at 1:10".to_string())
+    Token::Error("invalid processing instruction at 1:1 cause a non-XML character '\\0' found at 1:10".to_string())
 );
 
 test!(declaration_err_14, "<?xml version='1.0'encoding='UTF-8'?>",