Match gopkg.in/guregu/null.v3 version with k6

Considering the merge with k6, this will allow the final generated
binary to include a single version of the mentioned dependency.

go.mod

@@ -14,7 +14,7 @@ require (
 	go.k6.io/k6 v0.42.1-0.20230109152238-8418147fa630
 	golang.org/x/net v0.1.0
 	golang.org/x/sync v0.1.0
-	gopkg.in/guregu/null.v3 v3.5.0
+	gopkg.in/guregu/null.v3 v3.3.0
 )
 
 require (

go.sum

@@ -587,8 +587,8 @@ gopkg.in/check.v1 v1.0.0-20201130134442-10cb98267c6c h1:Hei/4ADfdWqJk1ZMxUNpqntN
 gopkg.in/check.v1 v1.0.0-20201130134442-10cb98267c6c/go.mod h1:JHkPIbrfpd72SG/EVd6muEfDQjcINNoR0C8j2r3qZ4Q=
 gopkg.in/errgo.v2 v2.1.0/go.mod h1:hNsd1EY+bozCKY1Ytp96fpM3vjJbqLJn88ws8XvfDNI=
 gopkg.in/fsnotify.v1 v1.4.7/go.mod h1:Tz8NjZHkW78fSQdbUxIjBTcgA1z1m8ZHf0WmKUhAMys=
-gopkg.in/guregu/null.v3 v3.5.0 h1:xTcasT8ETfMcUHn0zTvIYtQud/9Mx5dJqD554SZct0o=
-gopkg.in/guregu/null.v3 v3.5.0/go.mod h1:E4tX2Qe3h7QdL+uZ3a0vqvYwKQsRSQKM5V4YltdgH9Y=
+gopkg.in/guregu/null.v3 v3.3.0 h1:8j3ggqq+NgKt/O7mbFVUFKUMWN+l1AmT5jQmJ6nPh2c=
+gopkg.in/guregu/null.v3 v3.3.0/go.mod h1:E4tX2Qe3h7QdL+uZ3a0vqvYwKQsRSQKM5V4YltdgH9Y=
 gopkg.in/tomb.v1 v1.0.0-20141024135613-dd632973f1e7 h1:uRGJdciOHaEIrze2W8Q3AKkepLTh2hOroT7a+7czfdQ=
 gopkg.in/tomb.v1 v1.0.0-20141024135613-dd632973f1e7/go.mod h1:dt/ZhP58zS4L8KSrWDmTeBkI65Dw0HsyUHuEVlX15mw=
 gopkg.in/yaml.v2 v2.2.2/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=