github: bump the MSRV to 1.70.0

Due to an indirect dependency which fails with the following error on
1.65.0

---
error[E0658]: use of unstable library feature 'once_cell'
   --> /home/runner/.cargo/registry/src/github.com-1ecc6299db9ec823/ignore-0.4.21/src/gitignore.rs:596:9
    |
596 |     use std::sync::OnceLock;
    |         ^^^^^^^^^^^^^^^^^^^
    |
    = note: see issue #74465 <rust-lang/rust#74465> for more information

.github/workflows/ci.yml

@@ -21,7 +21,7 @@ jobs:
         rust:
           - stable
           - beta
-          - 1.65.0  # MSRV
+          - 1.70.0  # MSRV
         runs_on:
           - ubuntu-latest
           - windows-latest
@@ -42,7 +42,7 @@ jobs:
             rust: beta
           - runs_on: ubuntu-latest
             feature: net-tokio,socket2
-            rust: 1.65.0  # MSRV
+            rust: 1.70.0  # MSRV
     env:
       RUSTFLAGS: --deny warnings
     steps: