chore: Enforce min rustls version to 0.23.19

`rustls` versions 0.23.18 and 0.23.19 contains fix for vulnerability
RUSTSEC-2024-0399. However, 0.23.18 bumps MSRV to 1.71. 0.23.19 reverts
MSRV back to 1.63.

We enforce min `rustls` version to 0.23.19 to make it easier to compile
on MSRV and ensure we include the RUSTSEC-2024-0399 fix.

Note that in CI, I decided to pin `rustls` dependency to 0.23.19
explicitly. This is because in future versions of `rustls`, the MSRV
will be changed to 1.71.

.github/workflows/cont_integration.yml

@@ -31,7 +31,7 @@ jobs:
       - name: Pin dependencies for MSRV
         if: matrix.rust == '1.63.0'
         run: |
-          cargo update -p rustls --precise "0.23.17"
+          cargo update -p rustls --precise "0.23.19"
       - name: Test
         run: cargo test --verbose --all-features
       - name: Setup iptables for the timeout test

Cargo.toml

@@ -26,7 +26,7 @@ serde_json = { version = "^1.0" }
 
 # Optional dependencies
 openssl = { version = "0.10", optional = true }
-rustls = { version = "0.23", optional = true, default-features = false }
+rustls = { version = "0.23.19", optional = true, default-features = false }
 webpki-roots = { version = "0.25", optional = true }
 
 byteorder = { version = "1.0", optional = true }