set tested MSRV to 1.67 - the minimum required by time.

Thus, we set clippy to 1.70 because we can (and that was the goal
according to `helix` and is the MSRV of `home` (a cargo crate) too).

Once 1.67 isn't good enough anymore, we will update it to v1.70 so
everything matches once again. This is mainly for supporting rustsec
this one time.

Author: Byron

.github/workflows/msrv.yml

@@ -20,6 +20,6 @@ jobs:
     runs-on: ${{ matrix.os }}
     steps:
       - uses: actions/checkout@v3
-      - uses: dtolnay/rust-toolchain@1.70.0 # dictated by `firefox` to support the `helix` editor, IMPORTANT: adjust etc/msrv-badge.svg as well
+      - uses: dtolnay/rust-toolchain@1.67.0 # dictated by `firefox` to support the `helix` editor, but now driven by the `time` crate. IMPORTANT: adjust etc/msrv-badge.svg as well
       - uses: extractions/setup-just@v1
       - run: just ci-check-msrv