fix stray quote in test harness

Author: ExpHP

tests/integration/snapshots/integration__integration__show_instr_offsets__no_diffswitch_with_instr_offsets.snap

@@ -2,7 +2,7 @@
 source: tests/integration/show_instr_offsets.rs
 expression: decompiled
 ---
-#pragma mapfile "Xx_mapfile-1_xX""
+#pragma mapfile "Xx_mapfile-1_xX"
 
 script timeline0 {
  /* (0x7c) 0x0 */ }

tests/integration_impl/source_test.rs

@@ -451,7 +451,7 @@ fn make_decompiled_text_deterministic(text: &str) -> String {
             regex::RegexBuilder::new(r#"^(#pragma +(?:\w+ +)+)".+(Xx_.+_xX)"#).multi_line(true).build().unwrap()
         };
     }
-    TEMP_FILENAME_RE.replace_all(text, r#"$1"$2""#).into()
+    TEMP_FILENAME_RE.replace_all(text, r#"$1"$2"#).into()
 }
 
 struct SourceBuilder {