Fix missing rule "fstring-illegal-multi-brace".

Author: vpetrovykh

grammars/MagicPython.cson

@@ -27,6 +27,9 @@ patterns: [
   }
 ]
 repository:
+  impossible:
+    comment: "This is a special rule that should be used where no match is desired. It is not a good idea to match something like '1{0}' because in some cases that can result in infinite loops in token generation. So the rule instead matches and impossible expression to allow a mathc to fail and move to the next token."
+    match: "$.^"
   statement:
     patterns: [
       {
@@ -856,6 +859,12 @@ repository:
         include: "#f-expression"
       }
     ]
+  "fstring-illegal-multi-brace":
+    patterns: [
+      {
+        include: "#impossible"
+      }
+    ]
   "f-expression":
     comment: "All valid Python expressions, except comments and line cont"
     patterns: [

grammars/MagicPython.tmLanguage

@@ -41,6 +41,13 @@
     </array>
     <key>repository</key>
     <dict>
+      <key>impossible</key>
+      <dict>
+        <key>comment</key>
+        <string>This is a special rule that should be used where no match is desired. It is not a good idea to match something like '1{0}' because in some cases that can result in infinite loops in token generation. So the rule instead matches and impossible expression to allow a mathc to fail and move to the next token.</string>
+        <key>match</key>
+        <string>$.^</string>
+      </dict>
       <key>statement</key>
       <dict>
         <key>patterns</key>
@@ -1325,6 +1332,16 @@
           </dict>
         </array>
       </dict>
+      <key>fstring-illegal-multi-brace</key>
+      <dict>
+        <key>patterns</key>
+        <array>
+          <dict>
+            <key>include</key>
+            <string>#impossible</string>
+          </dict>
+        </array>
+      </dict>
       <key>f-expression</key>
       <dict>
         <key>comment</key>

grammars/src/MagicPython.syntax.yaml

@@ -207,6 +207,15 @@ repository:
         guard: ""
 
 
+  impossible:
+    comment: This is a special rule that should be used where no match
+             is desired. It is not a good idea to match something like
+             '1{0}' because in some cases that can result in infinite
+             loops in token generation. So the rule instead matches
+             and impossible expression to allow a mathc to fail and
+             move to the next token.
+    match: '$.^'
+
   statement:
     patterns:
       - include: '#import'
@@ -716,6 +725,10 @@ repository:
       - include: '#fstring-terminator-single'
       - include: '#f-expression'
 
+  fstring-illegal-multi-brace:
+    patterns:
+      - include: '#impossible'
+
   f-expression:
     comment: All valid Python expressions, except comments and line cont
     patterns: