Fix three typos in comments. NFC.

Author: gottesmm

include/swift/AST/ActorIsolation.h

@@ -180,7 +180,7 @@ class ActorIsolation {
     return parameterIndex;
   }
 
-  /// Returns true if this actor-instance isolation appllies to the self
+  /// Returns true if this actor-instance isolation applies to the self
   /// parameter of a method.
   bool isActorInstanceForSelfParameter() const {
     return getActorInstanceParameter() == 0;

lib/SILOptimizer/Utils/SILIsolationInfo.cpp

@@ -1167,7 +1167,7 @@ SILValue ActorInstance::lookThroughInsts(SILValue value) {
       continue;
     }
 
-    // Look Through extracting from optionals.
+    // Look through extracting from optionals.
     if (auto *uedi = dyn_cast<UncheckedEnumDataInst>(svi)) {
       if (uedi->getEnumDecl() ==
           uedi->getFunction()->getASTContext().getOptionalDecl()) {
@@ -1176,7 +1176,7 @@ SILValue ActorInstance::lookThroughInsts(SILValue value) {
       }
     }
 
-    // Look Through wrapping in an enum.
+    // Look through wrapping in an optional.
     if (auto *ei = dyn_cast<EnumInst>(svi)) {
       if (ei->hasOperand()) {
         if (ei->getElement()->getParentEnum() ==