Fix typos: alpah -> alpha

compiler/typecheck/TcHsSyn.hs

@@ -1618,7 +1618,7 @@ quantify over them.  Example:
 
   {-# RULES "myrule"  foo C = 1 #-}
 
-After type checking the LHS becomes (foo alpha (C alpah)) and we do
+After type checking the LHS becomes (foo alpha (C alpha)) and we do
 not want to zap the unbound meta-tyvar 'alpha' to Any, because that
 limits the applicability of the rule.  Instead, we want to quantify
 over it!

compiler/typecheck/TcSimplify.hs

@@ -1850,7 +1850,7 @@ Which equalities should we float?  We want to float ones where there
 is a decent chance that floating outwards will allow unification to
 happen.  In particular:
 
-   Float out equalities of form (alpaha ~ ty) or (ty ~ alpha), where
+   Float out equalities of form (alpha ~ ty) or (ty ~ alpha), where
 
    * alpha is a meta-tyvar.
 

testsuite/tests/indexed-types/should_compile/IndTypesPerfMerge.hs

@@ -86,8 +86,8 @@ Another solve path:
   ty := beta
   gamma := MergerType alpha beta
 
-  UnmergedLeft (MergerType alpah beta) ~ alpha
-  UnmergedRight (MergerType alpah beta) ~ beta
+  UnmergedLeft (MergerType alpha beta) ~ alpha
+  UnmergedRight (MergerType alpha beta) ~ beta
   Merger (MergerType alpha beta)
   Mergeable alpha beta