Fix CI: enable ICMP tests on Linux and fix gotestfmt on macOS/Windows

Three pre-existing issues prevented the Check workflow from passing:

1. Linux: ICMP tests fail because ping_group_range on GitHub Actions
   runners defaults to "1 0" (unprivileged ICMP disabled). Add sysctl
   step to allow unprivileged ICMP sockets.

2. macOS: go test -json emits linker warnings (LC_DYSYMTAB) as
   "Action":"build-output" JSON lines. gotestfmt v2.5.0 predates this
   action type (Go 1.21+) and panics in parseLine
   (gotesttools/gotestfmt#64). Filter build-output lines before piping
   to gotestfmt.

3. Windows: GO_TEST_LOG_OUTPUT pointed to /tmp/gotest.log which does
   not resolve through the MSYS2-to-native-Go boundary. Use relative
   path instead.

These failures were masked by fail-fast: Linux failed first (ICMP),
cancelling macOS and Windows before they reached gotestfmt.

.github/workflows/check.yaml

@@ -14,5 +14,8 @@ jobs:
         go-version: ${{ matrix.go-version }}
     - name: Checkout code
       uses: actions/checkout@v4
+    - name: Allow unprivileged ICMP (Linux)
+      if: runner.os == 'Linux'
+      run: sudo sysctl -w net.ipv4.ping_group_range="0 2147483647"
     - name: Test
       run: make test

.gitignore

@@ -14,6 +14,7 @@ cscope.*
 /packaging
 .DS_Store
 *-session.log
+gotest.log
 ssh_server_tests/.env
 /.cover
 built_artifacts/

Makefile

@@ -128,7 +128,7 @@ endif
 #for FIPS compliance, FPM defaults to MD5.
 RPM_DIGEST := --rpm-digest sha256
 
-GO_TEST_LOG_OUTPUT = /tmp/gotest.log
+GO_TEST_LOG_OUTPUT = gotest.log
 
 .PHONY: all
 all: cloudflared test
@@ -164,7 +164,7 @@ generate-docker-version:
 test: vet
 	$Q go test -json -v -mod=vendor -race $(LDFLAGS) ./... 2>&1 | tee $(GO_TEST_LOG_OUTPUT)
 ifneq ($(FIPS), true)
-	@go run -mod=readonly github.com/gotesttools/gotestfmt/v2/cmd/gotestfmt@latest -input $(GO_TEST_LOG_OUTPUT)
+	@grep -v '"Action":"build-output"' $(GO_TEST_LOG_OUTPUT) | go run -mod=readonly github.com/gotesttools/gotestfmt/v2/cmd/gotestfmt@latest
 endif
 
 .PHONY: cover