fix Markdown in the Lockable doc strings (#58603)

(cherry picked from commit 9da6455)

Author: nsajko

base/lock.jl

@@ -295,7 +295,7 @@ macro lock_nofail(l, expr)
 end
 
 """
-  Lockable(value, lock = ReentrantLock())
+    Lockable(value, lock = ReentrantLock())
 
 Creates a `Lockable` object that wraps `value` and
 associates it with the provided `lock`. This object
@@ -328,7 +328,7 @@ Lockable(value) = Lockable(value, ReentrantLock())
 getindex(l::Lockable) = (assert_havelock(l.lock); l.value)
 
 """
-  lock(f::Function, l::Lockable)
+    lock(f::Function, l::Lockable)
 
 Acquire the lock associated with `l`, execute `f` with the lock held,
 and release the lock when `f` returns. `f` will receive one positional