Fix another bad join

Before
```
[2023-03-01 08:19:51] Evaluated non-recursive predicate Filters#b57b2328::Filters::selfPostUpdate#2#ff@6718c917 in 6751ms (size: 83265).
Evaluated relational algebra for predicate Filters#b57b2328::Filters::selfPostUpdate#2#ff@6718c917 with tuple counts:
         3872025  ~3%    {2} r1 = JOIN _CfgNodes#ace8e412::ExprCfgNode::getExpr#0#dispred#ff_DataFlowPrivate#462ff392::Cached::TExprNode#ff#shared WITH Statement#f35022d0::Stmt::getCfgScope#0#dispred#ff ON FIRST 1 OUTPUT Rhs.1, Lhs.1
         3637917  ~0%    {2} r2 = JOIN r1 WITH Method#8b49e67f::Callable#f ON FIRST 1 OUTPUT Lhs.0, Lhs.1
          679799  ~0%    {2} r3 = JOIN r2 WITH Method#8b49e67f::Method#ff ON FIRST 1 OUTPUT Lhs.0, Lhs.1
         3069328  ~0%    {3} r4 = JOIN r3 WITH Variable#1965ffe5::Variable::getDeclaringScope#0#dispred#ff_10#join_rhs ON FIRST 1 OUTPUT Rhs.1, Lhs.1, Lhs.0
        22039083  ~0%    {3} r5 = JOIN r4 WITH Variable#1965ffe5::VariableAccess::getVariable#0#dispred#ff_10#join_rhs ON FIRST 1 OUTPUT Rhs.1, Lhs.1, Lhs.2
        10051483  ~0%    {3} r6 = JOIN r5 WITH Variable#9f7d933a::SelfVariableAccessImpl#class#f ON FIRST 1 OUTPUT Lhs.0, Lhs.1, Lhs.2
        10057538  ~5%    {3} r7 = JOIN r6 WITH CfgNodes#ace8e412::ExprCfgNode::getExpr#0#dispred#ff_10#join_rhs ON FIRST 1 OUTPUT Rhs.1, Lhs.1, Lhs.2
        10057538  ~5%    {3} r8 = JOIN r7 WITH CfgNodes#ace8e412::ExprNodes::SelfVariableAccessCfgNode#ff ON FIRST 1 OUTPUT Lhs.0, Lhs.1, Lhs.2
        10057538  ~0%    {3} r9 = JOIN r8 WITH DataFlowPrivate#462ff392::Cached::TExprNode#ff ON FIRST 1 OUTPUT Rhs.1, Lhs.1, Lhs.2
        1003393  ~1%    {3} r10 = JOIN r9 WITH DataFlowPublic#e1781e31::PostUpdateNode::getPreUpdateNode#0#dispred#ff_10#join_rhs ON FIRST 1 OUTPUT Rhs.1, Lhs.1, Lhs.2
           83281  ~2%    {2} r11 = JOIN r10 WITH DataFlowPublic#e1781e31::PostUpdateNode::getPreUpdateNode#0#dispred#ff ON FIRST 2 OUTPUT Lhs.0, Lhs.2
                         return r11
```

After
```
[2023-03-01 08:31:20] Evaluated non-recursive predicate Filters#b57b2328::Filters::selfPostUpdate#2#ff@06d73c6q in 161ms (size: 83265).
Evaluated relational algebra for predicate Filters#b57b2328::Filters::selfPostUpdate#2#ff@06d73c6q with tuple counts:
         23680  ~2%    {1} r1 = SCAN Method#8b49e67f::Method#ff OUTPUT In.0
         23680  ~2%    {1} r2 = STREAM DEDUP r1
         23680  ~0%    {2} r3 = JOIN r2 WITH Method#8b49e67f::Callable#f ON FIRST 1 OUTPUT Lhs.0, Lhs.0
         54790  ~4%    {3} r4 = JOIN r3 WITH Variable#1965ffe5::Variable::getDeclaringScope#0#dispred#ff_10#join_rhs ON FIRST 1 OUTPUT Rhs.1, Lhs.1, Lhs.0
        202490  ~0%    {3} r5 = JOIN r4 WITH Variable#1965ffe5::VariableAccess::getVariable#0#dispred#ff_10#join_rhs ON FIRST 1 OUTPUT Rhs.1, Lhs.1, Lhs.2
         98332  ~5%    {3} r6 = JOIN r5 WITH Variable#9f7d933a::SelfVariableAccessImpl#class#f ON FIRST 1 OUTPUT Lhs.0, Lhs.1, Lhs.2
         83491  ~1%    {2} r7 = JOIN r6 WITH Statement#f35022d0::Stmt::getCfgScope#0#dispred#ff ON FIRST 2 OUTPUT Lhs.0, Lhs.2
         83584  ~0%    {2} r8 = JOIN r7 WITH CfgNodes#ace8e412::ExprCfgNode::getExpr#0#dispred#ff_10#join_rhs ON FIRST 1 OUTPUT Rhs.1, Lhs.1
         83584  ~0%    {2} r9 = JOIN r8 WITH DataFlowPrivate#462ff392::Cached::TExprNode#ff ON FIRST 1 OUTPUT Rhs.1, Lhs.1
         83265  ~2%    {2} r10 = JOIN r9 WITH DataFlowPublic#e1781e31::PostUpdateNode::getPreUpdateNode#0#dispred#ff_10#join_rhs ON FIRST 1 OUTPUT Rhs.1, Lhs.1
                       return r10
```

Author: hvitved

ruby/ql/lib/codeql/ruby/frameworks/actioncontroller/Filters.qll

@@ -402,13 +402,11 @@ module Filters {
    * Holds if `n` is a post-update node for `self` in method `m`.
    */
   private predicate selfPostUpdate(DataFlow::PostUpdateNode n, Method m) {
-    m = n.getPreUpdateNode().asExpr().getExpr().getEnclosingCallable() and
-    n.getPreUpdateNode()
-        .asExpr()
-        .(SelfVariableAccessCfgNode)
-        .getExpr()
-        .getVariable()
-        .getDeclaringScope() = m
+    n.getPreUpdateNode().asExpr().getExpr() =
+      any(SelfVariableAccess self |
+        pragma[only_bind_into](m) = self.getEnclosingCallable() and
+        self.getVariable().getDeclaringScope() = m
+      )
   }
 
   /**