test and build against both supported Go lines

The go directive is the compatibility floor, not the toolchain to
validate or ship with. Tests and the goreleaser dry run now run a
matrix over 1.25 and 1.26: the floor proves go install works for the
oldest supported toolchain, the newest is what releases build with.

The publishing build pins 1.26 explicitly -- with the directive
lowered, go-version-file would have silently downgraded official
binaries to the floor toolchain. Lint stays on the floor, where
typechecking is strictest for the module's declared language version.

Author: xobotyi

.github/workflows/ci.yml

@@ -29,24 +29,32 @@ jobs:
       fail-fast: false
       matrix:
         os: [ubuntu-latest, macos-latest, windows-latest]
+        # The floor declared by go.mod and the newest stable line: the floor
+        # proves go install works for the oldest supported toolchain, the
+        # newest is what releases build with.
+        go: ["1.25", "1.26"]
     runs-on: ${{ matrix.os }}
     steps:
       - uses: actions/checkout@v7
       - uses: actions/setup-go@v6
         with:
-          go-version-file: go.mod
+          go-version: ${{ matrix.go }}
       - run: go build ./...
       - run: go test -race ./...
 
   release-dry-run:
+    strategy:
+      fail-fast: false
+      matrix:
+        go: ["1.25", "1.26"]
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v7
         with:
           fetch-depth: 0
       - uses: actions/setup-go@v6
         with:
-          go-version-file: go.mod
+          go-version: ${{ matrix.go }}
       - uses: docker/setup-qemu-action@v4
       - uses: docker/setup-buildx-action@v4
       - uses: goreleaser/goreleaser-action@v7

.github/workflows/release.yml

@@ -20,7 +20,10 @@ jobs:
           fetch-depth: 0
       - uses: actions/setup-go@v6
         with:
-          go-version-file: go.mod
+          # Pinned to the newest CI-tested line rather than go.mod: the
+          # directive there is the compatibility floor, not the toolchain
+          # official binaries should be built with.
+          go-version: "1.26"
           # Release builds are hermetic: the Actions cache is writable from
           # any PR branch, so restoring it here would let a poisoned cache
           # entry reach the publishing build.