Account for possible cache invalidation on a different thread in assert.

Attempt at fixing #59395. Reviewing the codepath I don't see any other obvious points that could cause the assert to fail, so if it continues to reproduce after this change we can look at further logging to determine the root cause.

src/Compilers/Core/Portable/Compilation/Compilation.cs

@@ -1169,7 +1169,9 @@ public INamedTypeSymbol CreateNativeIntegerTypeSymbol(bool signed)
             {
                 val = CommonGetTypeByMetadataName(fullyQualifiedMetadataName);
                 var result = _getTypeCache.TryAdd(fullyQualifiedMetadataName, val);
-                Debug.Assert(result || (_getTypeCache.TryGetValue(fullyQualifiedMetadataName, out var addedType) && ReferenceEquals(addedType, val)));
+                Debug.Assert(result
+                 || !_getTypeCache.TryGetValue(fullyQualifiedMetadataName, out var addedType) // Could fail if the type was already evicted from the cache
+                 || ReferenceEquals(addedType, val));
             }
             return val;
         }
@@ -1196,8 +1198,8 @@ public ImmutableArray<INamedTypeSymbol> GetTypesByMetadataName(string fullyQuali
                 val = getTypesByMetadataNameImpl();
                 var result = _getTypesCache.TryAdd(fullyQualifiedMetadataName, val);
                 Debug.Assert(result
-                    || (_getTypesCache.TryGetValue(fullyQualifiedMetadataName, out var addedArray)
-                        && Enumerable.SequenceEqual(addedArray, val, ReferenceEqualityComparer.Instance)));
+                    || !_getTypesCache.TryGetValue(fullyQualifiedMetadataName, out var addedArray) // Could fail if the type was already evicted from the cache
+                    || Enumerable.SequenceEqual(addedArray, val, ReferenceEqualityComparer.Instance));
             }
 
             return val;