Fix JET errors around matching methods for lock(...) and unlock(...) (#167)

```
┌ put_ref(rid::Distributed.RRID, caller::Int64, args::WeakRef) @ Distributed /workpath/Distributed.jl/src/remotecall.jl:709
│ no matching method found `lock(::Nothing)` (1/2 union split): Distributed.lock((rv::Distributed.RemoteValue).synctake::Union{Nothing, ReentrantLock})
└────────────────────
```

```
┌ put_ref(rid::Distributed.RRID, caller::Int64, args::WeakRef) @ Distributed /workpath/Distributed.jl/src/remotecall.jl:710
│ no matching method found `unlock(::Nothing)` (1/2 union split): Distributed.unlock((rv::Distributed.RemoteValue).synctake::Union{Nothing, ReentrantLock})
││││││││││││││└────────────────────
```

```
┌ take_ref(rid::Any, caller::Any, args::Vararg{Any}) @ Distributed /workpath/Distributed.jl/src/remotecall.jl:734
│ no matching method found `lock(::Nothing)` (1/2 union split): Distributed.lock((rv::Distributed.RemoteValue).synctake::Union{Nothing, ReentrantLock})
└────────────────────
```

```
┌ take_ref(rid::Any, caller::Any, args::Vararg{Any}) @ Distributed /workpath/Distributed.jl/src/remotecall.jl:742
│ no matching method found `unlock(::Nothing)` (1/2 union split): Distributed.unlock((rv::Distributed.RemoteValue).synctake::Union{Nothing, ReentrantLock})
└────────────────────
```

```
┌ (::Distributed.var"#handle_msg##2#handle_msg##3"{Distributed.CallMsg{…}, Distributed.MsgHeader, Base.PipeEndpoint})() @ Distributed /workpath/Distributed.jl/src/process_messages.jl:292
│ no matching method found `unlock(::Nothing)` (1/2 union split): Distributed.unlock(((v::Distributed.SyncTake).rv::Distributed.RemoteValue).synctake::Union{Nothing, ReentrantLock})
└────────────────────
```

(cherry picked from commit 01027d1)

Author: DilumAluthge

src/process_messages.jl

@@ -289,7 +289,7 @@ function handle_msg(msg::CallMsg{:call_fetch}, header, r_stream, w_stream, versi
             try
                 deliver_result(w_stream, :call_fetch, header.notify_oid, v.v)
             finally
-                unlock(v.rv.synctake)
+                unlock(v.rv.synctake::ReentrantLock)
             end
         else
             deliver_result(w_stream, :call_fetch, header.notify_oid, v)

src/remotecall.jl

@@ -706,8 +706,8 @@ function put_ref(rid, caller, args...)
     put!(rv, args...)
     if myid() == caller && rv.synctake !== nothing
         # Wait till a "taken" value is serialized out - github issue #29932
-        lock(rv.synctake)
-        unlock(rv.synctake)
+        lock(rv.synctake::ReentrantLock)
+        unlock(rv.synctake::ReentrantLock)
     end
     nothing
 end
@@ -731,15 +731,15 @@ function take_ref(rid, caller, args...)
         # special handling for local put! / remote take! on unbuffered channel
         # github issue #29932
         synctake = true
-        lock(rv.synctake)
+        lock(rv.synctake::ReentrantLock)
     end
 
     v = try
         take!(rv, args...)
     catch e
         # avoid unmatched unlock when exception occurs
         # github issue #33972
-        synctake && unlock(rv.synctake)
+        synctake && unlock(rv.synctake::ReentrantLock)
         rethrow(e)
     end