How do I add variables to expression

[moluzhui]

Describe the bug
A clear and concise description of what the bug is.

Note that any how to questions should be posted in the discussion board and not raised as an issue.

Version of yq: 4.14.1
Operating system: mac/linux/windows/....
Installed via: docker/binary release/homebrew/snap/...

Input Yaml
Concise yaml document(s) (as simple as possible to show the bug, please keep it to 10 lines or less)
data1.yml:

test1: test1
test2:
  subtest2: test2

Command
The command you ran:

test3="test3"
yq e -i '.test2.subtest2= \"${test3}\"' data1.yml

Actual behavior

Error: Parsing expression: Lexer error: could not match text starting at 1:18 failing at 1:19.
        unmatched text: "\\"

Expected behavior

test1: test1
test2:
  subtest2: test3

Additional context
Add any other context about the problem here.
Centos 7

[mikefarah]

Best way to do it is using the env operator:

https://mikefarah.gitbook.io/yq/operators/env-variable-operators#read-string-environment-variable