htlcswitch+go.mod: use updated fn.ContextGuard

This commit updates the fn dep to the version containing the updates to
the ContextGuard implementation. Only the htlcswitch/link uses the guard
at the moment so this is updated to make use of the new implementation.

Author: ellemouton

go.mod

@@ -36,7 +36,7 @@ require (
 	github.com/lightningnetwork/lightning-onion v1.2.1-0.20240712235311-98bd56499dfb
 	github.com/lightningnetwork/lnd/cert v1.2.2
 	github.com/lightningnetwork/lnd/clock v1.1.1
-	github.com/lightningnetwork/lnd/fn/v2 v2.0.4
+	github.com/lightningnetwork/lnd/fn/v2 v2.0.8
 	github.com/lightningnetwork/lnd/healthcheck v1.2.6
 	github.com/lightningnetwork/lnd/kvdb v1.4.12
 	github.com/lightningnetwork/lnd/queue v1.1.1

go.sum

@@ -456,8 +456,8 @@ github.com/lightningnetwork/lnd/cert v1.2.2 h1:71YK6hogeJtxSxw2teq3eGeuy4rHGKcFf
 github.com/lightningnetwork/lnd/cert v1.2.2/go.mod h1:jQmFn/Ez4zhDgq2hnYSw8r35bqGVxViXhX6Cd7HXM6U=
 github.com/lightningnetwork/lnd/clock v1.1.1 h1:OfR3/zcJd2RhH0RU+zX/77c0ZiOnIMsDIBjgjWdZgA0=
 github.com/lightningnetwork/lnd/clock v1.1.1/go.mod h1:mGnAhPyjYZQJmebS7aevElXKTFDuO+uNFFfMXK1W8xQ=
-github.com/lightningnetwork/lnd/fn/v2 v2.0.4 h1:DiC/AEa7DhnY4qOEQBISu1cp+1+51LjbVDzNLVBwNjI=
-github.com/lightningnetwork/lnd/fn/v2 v2.0.4/go.mod h1:TOzwrhjB/Azw1V7aa8t21ufcQmdsQOQMDtxVOQWNl8s=
+github.com/lightningnetwork/lnd/fn/v2 v2.0.8 h1:r2SLz7gZYQPVc3IZhU82M66guz3Zk2oY+Rlj9QN5S3g=
+github.com/lightningnetwork/lnd/fn/v2 v2.0.8/go.mod h1:TOzwrhjB/Azw1V7aa8t21ufcQmdsQOQMDtxVOQWNl8s=
 github.com/lightningnetwork/lnd/healthcheck v1.2.6 h1:1sWhqr93GdkWy4+6U7JxBfcyZIE78MhIHTJZfPx7qqI=
 github.com/lightningnetwork/lnd/healthcheck v1.2.6/go.mod h1:Mu02um4CWY/zdTOvFje7WJgJcHyX2zq/FG3MhOAiGaQ=
 github.com/lightningnetwork/lnd/kvdb v1.4.12 h1:Y0WY5Tbjyjn6eCYh068qkWur5oFtioJlfxc8w5SlJeQ=