Fix nondeterministic behavior (#9341)

The underlying implementation of os.exec uses channels and goroutines.
It is possible to have time-variant error values returned from Cmd.Wait
depending on which comes first.

Also, the git subcommand and options should be separated tokens.

Fixes a flaky test in modules/git/command_test.go

modules/git/command.go

@@ -138,7 +138,7 @@ func (c *Command) RunInDirTimeoutEnvFullPipelineFunc(env []string, timeout time.
 		fn(ctx, cancel)
 	}
 
-	if err := cmd.Wait(); err != nil {
+	if err := cmd.Wait(); err != nil && ctx.Err() != context.DeadlineExceeded {
 		return err
 	}