ci: keep status check names stable across Go version bumps

Job had no explicit name, so GitHub derived the check name from the job
id plus matrix values (`test (1.26, ubuntu-latest)`). Branch protection
matches contexts by exact string, so every Go version bump renamed the
checks and left the required contexts stale — and a required context
that is never reported blocks the PR silently as "Expected", rather
than failing.

Drop go-version from the matrix and read it from go.mod instead, so the
check names become `test (ubuntu-latest)` / `test (macos-latest)` and no
longer track the toolchain version. go.mod already pins go 1.26, so the
Go version in CI is unchanged.

Also move checkout ahead of setup-go, which go-version-file requires,
add fail-fast: false so one platform failing no longer cancels the other
before its logs are available, and bump checkout v4 -> v7 and setup-go
v5 -> v7.

Required status checks must be updated to the new names after this
merges, otherwise every later PR stays pending.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Author: kkweon

.github/workflows/ci.yaml

@@ -7,19 +7,17 @@ name: CI
 jobs:
   test:
     strategy:
+      fail-fast: false
       matrix:
-        go-version:
-          - '1.26'
         os:
           - ubuntu-latest
           - macos-latest
     runs-on: ${{ matrix.os }}
     steps:
-      - name: Install Go ${{ matrix.go-version }}
-        uses: actions/setup-go@v5
+      - uses: actions/checkout@v7
+      - name: Install Go
+        uses: actions/setup-go@v7
         with:
-          go-version: ${{ matrix.go-version }}
-      - uses: actions/checkout@v4
+          go-version-file: go.mod
       - run: make install-kiwi
       - run: make test
-