action.yml: unset GOOS/GOARCH when installing govulncheck

When a caller sets GOOS=windows at the job level (e.g.
prometheus/windows_exporter, which builds for Windows but runs
CI on Linux), go install would build govulncheck for Windows
instead of the Linux runner, causing "command not found" on
execution.

Clearing GOOS and GOARCH in the install step ensures the tool
is always built for the host platform.

Change-Id: Ied55d19c2f0e733f7882e1f1348db2c4c9f38f1d
GitHub-Last-Rev: b5c359d5956ae33a422e0ed76106f6cf3e63cb89
GitHub-Pull-Request: golang/govulncheck-action#9
Reviewed-on: https://go-review.googlesource.com/c/govulncheck-action/+/785640
Auto-Submit: Sean Liao <sean@liao.dev>
TryBot-Bypass: Sean Liao <sean@liao.dev>
Reviewed-by: Hyang-Ah Hana Kim <hyangah@gmail.com>
Auto-Submit: Hyang-Ah Hana Kim <hyangah@gmail.com>
Reviewed-by: Sean Liao <sean@liao.dev>
Reviewed-by: Cherry Mui <cherryyz@google.com>
diff --git a/action.yml b/action.yml
index 9f5016e..7a33d71 100644
--- a/action.yml
+++ b/action.yml
@@ -55,6 +55,9 @@
     - name: Install govulncheck
       run: go install golang.org/x/vuln/cmd/govulncheck@latest
       shell: bash
+      env:
+        GOOS: ''
+        GOARCH: ''
     - if: inputs.output-file == ''
       name: Run govulncheck
       run: govulncheck -C ${{ inputs.work-dir }} -format ${{ inputs.output-format }} ${{ inputs.go-package }}