ci: move the TinyGo gate to 0.42.0 (#909)

* ci: move the TinyGo gate to 0.42.0

tinygo-wasi-build installed 0.41.1 (released 2026-04-22); 0.42.0 has been out
since 2026-09-01, so the gate validated against a toolchain one release behind.

0.42.0 carries tinygo-org/tinygo#5401 (file-level //go:linkname), which removes
the x/sys link failure on native darwin — one of the three #547 names. The other
two are tinygo-org/tinygo#4794, still open, so native macOS still does not link.

Verified on darwin/arm64: the wasi build and boot both succeed, and a 69-case
differential corpus is identical to the stdgo runtime and to 0.41.1 despite the
LLVM 20.1.1 -> 22.1.4 jump.

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

* ci: clarify TinyGo gate scope

---------

Co-authored-by: Claude Opus 5 <noreply@anthropic.com>

Author: mparrett

.github/workflows/go.yml

@@ -224,10 +224,12 @@ jobs:
         uses: actions/setup-go@v6
         with:
           go-version-file: go.mod
+      # Pin TinyGo so a new release cannot turn this gate red on its own;
+      # bump deliberately and let this job verify the WASI build and core boot.
       - name: Install TinyGo
         run: |
-          wget -q https://github.com/tinygo-org/tinygo/releases/download/v0.41.1/tinygo_0.41.1_amd64.deb
-          sudo dpkg -i tinygo_0.41.1_amd64.deb
+          wget -q https://github.com/tinygo-org/tinygo/releases/download/v0.42.0/tinygo_0.42.0_amd64.deb
+          sudo dpkg -i tinygo_0.42.0_amd64.deb
       # Fetch directly: install.sh can exit 0 after a failed download, masking
       # transient CDN errors until the later PATH check (#682).
       - name: Install wasmtime