internal/lsp: use exec.CommandContext when running vulncheck

That, hopefully, handles process termination upon context
cancellation. (not 100% guaranteed)

Change-Id: I79441afb794c37e9e55f710f124871a82aa4effe
Reviewed-on: https://go-review.googlesource.com/c/tools/+/420997
Reviewed-by: Suzy Mueller <[email protected]>
Reviewed-by: Robert Findley <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Run-TryBot: Hyang-Ah Hana Kim <[email protected]>
gopls-CI: kokoro <[email protected]>

Author: hyangah

internal/lsp/command.go

@@ -817,7 +817,7 @@ func (c *commandHandler) RunVulncheckExp(ctx context.Context, args command.Vulnc
 			return errors.New("vulncheck feature is not available")
 		}
 
-		cmd := exec.Command(os.Args[0], "vulncheck", "-config", args.Pattern)
+		cmd := exec.CommandContext(ctx, os.Args[0], "vulncheck", "-config", args.Pattern)
 		cmd.Dir = filepath.Dir(args.URI.SpanURI().Filename())
 
 		var viewEnv []string