ci: disable the unsafe-pinned feature in the MSRV workflow

The MSRV only holds when crate-unstable features aren't used.
`unsafe-pinned` is an unstable feature as mentioned in the README, but
it hasn't been disabled for this test (that's because it didn't trigger
before, since there was no stable version containing the feature).

Signed-off-by: Benno Lossin <lossin@kernel.org>

Author: BennoLossin

.github/workflows/ci.yml

@@ -161,7 +161,7 @@ jobs:
       - uses: dtolnay/rust-toolchain@stable
       - run: cargo install cargo-hack
       - run: git config user.name "github-runner" && git config user.email "<>"
-      - run: git rebase --exec 'cargo hack --clean-per-run --feature-powerset --exclude-features alloc --exclude-features default --version-range 1.82.. --clean-per-version check --locked --all-targets' --exec 'cargo clean' --root
+      - run: git rebase --exec 'cargo hack --clean-per-run --feature-powerset --exclude-features unsafe-pinned --exclude-features alloc --exclude-features default --version-range 1.82.. --clean-per-version check --locked --all-targets' --exec 'cargo clean' --root
         env:
           RUSTFLAGS: "-Dwarnings"
   nightly-msrv: