Bump toolchain version by 1 day

The old `cargo-3ds` we were using didn't care about the commit date being 05-30, but the new one used by the `test-runner` action does.

Since the rustc version is one day older than the toolchain date, we should be able to work with just the 06-01 toolchain instead.

.github/workflows/ci.yml

@@ -20,8 +20,8 @@ jobs:
     strategy:
       matrix:
         toolchain:
-          # Run against a "known good" nightly
+          # Run against a "known good" nightly. Rustc version is 1 day behind the toolchain date
-          - nightly-2023-05-31
+          - nightly-2023-06-01
           # Check for breakage on latest nightly
           - nightly
 
@@ -58,7 +58,7 @@ jobs:
     strategy:
       matrix:
         toolchain:
-          - nightly-2023-05-31
+          - nightly-2023-06-01
           - nightly
     continue-on-error: ${{ matrix.toolchain == 'nightly' }}
     runs-on: ubuntu-latest