Merge #1524: ci: pin tokio to 1.38.1 to support MSRV 1.63

28d7530 ci: pin tokio to 1.38.1 to support MSRV 1.63 (Steve Myers)

Pull request description:

  ### Description

  The latest tokio minor version update from 1.38.1 to 1.39.1 changed it's MSRV from 1.63.0 to 1.70.0, breaking our CI MSRV 1.63 testing. This PR pins `tokio` back to 1.38.1 for our CI MSRV testing.

  ### Notes to the reviewers

  tokio-rs/tokio#6645

  https://crates.io/crates/tokio/versions

  ### Checklists

  #### All Submissions:

  * [x] I've signed all my commits
  * [x] I followed the [contribution guidelines](https://github.com/bitcoindevkit/bdk/blob/master/CONTRIBUTING.md)
  * [x] I ran `cargo fmt` and `cargo clippy` before committing

ACKs for top commit:
  LagginTimes:
    ACK 28d7530
  ValuedMammal:
    ACK 28d7530
  oleonardolima:
    ACK 28d7530

Tree-SHA512: 9eef750422cb8c3faa15771438e790afae44362d7c77e1d36cf70816ac7dabdd2e408e14502836ec86f845a2f1fe82905000c681fb6b4e873b036a41a280abd9

Author: notmandatory

.github/workflows/cont_integration.yml

@@ -36,6 +36,7 @@ jobs:
           cargo update -p proptest --precise "1.2.0"
           cargo update -p url --precise "2.5.0"
           cargo update -p cc --precise "1.0.105"
+          cargo update -p tokio --precise "1.38.1"
       - name: Build
         run: cargo build ${{ matrix.features }}
       - name: Test

README.md

@@ -74,6 +74,7 @@ cargo update -p home --precise "0.5.5"
 cargo update -p proptest --precise "1.2.0"
 cargo update -p url --precise "2.5.0"
 cargo update -p cc --precise "1.0.105"
+cargo update -p tokio --precise "1.38.1"
 ```
 
 ## License