cmd/govulncheck: do not shadow err in doGovulncheck.
cmd/govulncheck: do not shadow err in doGovulncheck.

Removes shadowing of the err variable in doGovulncheck.
May be involved with the nil pointer dereference in golang/go#56689.

Updates golang/go#56689

Change-Id: I805c9106f08dffda73efcd04e7a418b0ac8f64d2
Reviewed-on: https://go-review.googlesource.com/c/vuln/+/449675
Reviewed-by: Jonathan Amsterdam <e3d3698b2ccd5955e4adf250d0785062d0f9018b@google.com>
TryBot-Result: Gopher Robot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Zvonimir Pavlinovic <490af24f3def1258d2f7e9b10b20e341f6c68320@google.com>
Run-TryBot: Tim King <ee8a1d1efb05d8171fc0140ced15d455e83941c5@google.com>

golang/vuln,golang/vuln