Build tweaks

- Update dev-dependencies MSRV to 1.70.0
- Run cargo update to avoid errors using a Cargo.lock from the CI cache

.circleci/config.yml

@@ -20,7 +20,7 @@ workflows:
               # get a nightly or stable toolchain via rustup instead of a mutable docker tag
               toolchain_override: [
                 '__msrv__', # won't add any other toolchains, just uses what's in the docker image
-                '1.65.0', # minimum needed to build dev-dependencies
+                '1.70.0', # minimum needed to build dev-dependencies
                 'stable',
                 'beta',
                 'nightly'
@@ -50,6 +50,12 @@ jobs:
       - run:
           name: Log rustc version
           command: rustc --version
+      - run:
+          name: Build main target
+          # update first to select dependencies appropriate for this toolchain
+          command: |
+            cargo update
+            cargo build
       - run:
           name: Check formatting
           command: |
@@ -64,9 +70,6 @@ jobs:
               rustup component add clippy
               cargo clippy --all-targets
             fi
-      - run:
-          name: Build main target
-          command: cargo build
       - run:
           name: Build all targets
           command: |

Cargo.toml

@@ -10,7 +10,7 @@ keywords = ["base64", "utf8", "encode", "decode", "no_std"]
 categories = ["encoding"]
 license = "MIT OR Apache-2.0"
 edition = "2018"
-# dev-dependencies require 1.65, but the main code doesn't
+# dev-dependencies require 1.70, but the main code doesn't
 # This option was added in 1.56, keep it for when we bump MSRV.
 rust-version = "1.48.0"