ci: update maintainer-tools version

I believe that our previous use of the `rev:` key had no effect. We need
to use `ref:` with a full commit ID. As written, I think that we were
just always pulling master, even though it looked like a commit ID.

Anyway we don't use any cool features of rust-bitcoin-maintainer-tools
so it doesn't really matter here. But we should pin it properly.

Author: apoelstra

.github/workflows/rust.yml

@@ -23,7 +23,7 @@ jobs:
         uses: actions/checkout@v4
         with:
           repository: rust-bitcoin/rust-bitcoin-maintainer-tools
-          rev: b2ac115
+          ref: c3324024ced9bb1eb854397686919c3ff7d97e1e
           path: maintainer-tools
       - name: "Select toolchain"
         uses: dtolnay/rust-toolchain@stable
@@ -46,7 +46,7 @@ jobs:
         uses: actions/checkout@v4
         with:
           repository: rust-bitcoin/rust-bitcoin-maintainer-tools
-          rev: b2ac115
+          ref: c3324024ced9bb1eb854397686919c3ff7d97e1e
           path: maintainer-tools
       - name: "Select toolchain"
         uses: dtolnay/rust-toolchain@nightly
@@ -69,7 +69,7 @@ jobs:
         uses: actions/checkout@v4
         with:
           repository: rust-bitcoin/rust-bitcoin-maintainer-tools
-          rev: b2ac115
+          ref: c3324024ced9bb1eb854397686919c3ff7d97e1e
           path: maintainer-tools
       - name: "Select toolchain"
         uses: dtolnay/rust-toolchain@stable
@@ -94,7 +94,7 @@ jobs:
         uses: actions/checkout@v4
         with:
           repository: rust-bitcoin/rust-bitcoin-maintainer-tools
-          rev: b2ac115
+          ref: c3324024ced9bb1eb854397686919c3ff7d97e1e
           path: maintainer-tools
       - name: "Select toolchain"
         uses: dtolnay/rust-toolchain@nightly
@@ -119,7 +119,7 @@ jobs:
         uses: actions/checkout@v4
         with:
           repository: rust-bitcoin/rust-bitcoin-maintainer-tools
-          rev: b2ac115
+          ref: c3324024ced9bb1eb854397686919c3ff7d97e1e
           path: maintainer-tools
       - name: "Select toolchain"
         uses: dtolnay/rust-toolchain@stable
@@ -142,7 +142,7 @@ jobs:
         uses: actions/checkout@v4
         with:
           repository: rust-bitcoin/rust-bitcoin-maintainer-tools
-          rev: b2ac115
+          ref: c3324024ced9bb1eb854397686919c3ff7d97e1e
           path: maintainer-tools
       - name: "Select toolchain"
         uses: dtolnay/rust-toolchain@nightly
@@ -165,7 +165,7 @@ jobs:
         uses: actions/checkout@v4
         with:
           repository: rust-bitcoin/rust-bitcoin-maintainer-tools
-          rev: b2ac115
+          ref: c3324024ced9bb1eb854397686919c3ff7d97e1e
           path: maintainer-tools
       - name: "Select toolchain"
         uses: dtolnay/rust-toolchain@nightly