double slash in paths is a syntax error

Author: domenkozar

src/tokenizer.rs

@@ -172,6 +172,8 @@ impl Tokenizer<'_> {
             self.ctx.push(Context::InterpolStart);
         } else if self.str_since(past).ends_with('/') {
             return TOKEN_ERROR;
+        } else if self.str_since(past).contains("//") {
+            return TOKEN_ERROR;
         } else {
             self.pop_ctx(Context::Path);
         }

test_data/parser/error/path_double_slash.expect

@@ -0,0 +1,5 @@
+error: unexpected TOKEN_ERROR at 0..9, wanted any of [TOKEN_L_PAREN, TOKEN_REC, TOKEN_L_BRACE, TOKEN_L_BRACK, TOKEN_STRING_START, TOKEN_IDENT]
+[email protected]
+  [email protected]
+    [email protected] "/foo//bar"
+

test_data/parser/error/path_double_slash.nix

@@ -0,0 +1 @@
+/foo//bar