ci: Fix build for MSRV

Author: stevenroose

.github/workflows/rust.yml

@@ -21,7 +21,9 @@ jobs:
                   profile: minimal
                   toolchain: ${{ matrix.rust }}
                   override: true
-            - run: cargo update -p serde --precise 1.0.152
+            - run: cargo update --package backtrace --precise 0.3.50
+            - run: cargo update --package async-trait --precise 0.1.53
+            - run: cargo update --package serde --precise 1.0.152
             - name: Running test script
               run: ./contrib/test.sh