Merge pull request lightningdevkit#3953 from tnull/2025-07-drop-incremental-mutants

Drop `incremental-mutants` CI job (main)

Author: TheBlueMatt

.github/workflows/build.yml

@@ -219,9 +219,9 @@ jobs:
           git fetch upstream
           export GIT_COMMITTER_EMAIL="[email protected]"
           export GIT_COMMITTER_NAME="RL CI"
-          git rebase upstream/main
+          git rebase upstream/${{ github.base_ref }}
       - name: For each commit, run cargo check (including in fuzz)
-        run: ci/check-each-commit.sh upstream/main
+        run: ci/check-each-commit.sh upstream/${{ github.base_ref }}
 
   check_release:
     runs-on: ubuntu-latest
@@ -305,20 +305,3 @@ jobs:
           rustup component add rustfmt
       - name: Run rustfmt checks
         run: cargo fmt --check
-
-  incremental-mutants:
-    runs-on: ubuntu-latest
-    if: github.ref_name != 'main' # `main` has no diff with itself
-    steps:
-      - uses: actions/checkout@v4
-        with:
-          fetch-depth: 0
-      - name: Relative diff
-        run: |
-          git branch -av
-          git diff origin/main.. | tee git.diff
-      - uses: Swatinem/rust-cache@v2
-      - name: Mutants
-        run: |
-          cargo install cargo-mutants
-          cargo mutants --no-shuffle -j 2 -vV --in-diff git.diff