deps: bump crossbeam-epoch 0.9.18 → 0.9.20

Fixes RUSTSEC-2026-0204 — unsoundness in crossbeam-epoch < 0.9.20.
crossbeam-epoch is a transitive dependency pulled in via:
  crossbeam 0.8.4 → ttrpc 0.8.6

No direct dependency changes are needed; pinning the resolved version
in Cargo.lock is sufficient to ensure the fixed crate is used.

Ref: https://osv.dev/RUSTSEC-2026-0204

Generated-by: IBM Bob
Signed-off-by: stevenhorsman <steven@uk.ibm.com>

Cargo.lock

@@ -1345,9 +1345,9 @@ dependencies = [
 
 [[package]]
 name = "crossbeam-epoch"
-version = "0.9.18"
+version = "0.9.20"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "5b82ac4a3c2ca9c3460964f020e1402edd5753411d7737aa39c3714ad1b5420e"
+checksum = "2d6914041f254d6e9176c01941b21115dcfb7089e55135a35411081bd106ef3f"
 dependencies = [
  "crossbeam-utils",
 ]