[envvars] Fix error when env contains Bash function

[apgrucza]

Summary

Fixes #995 - Error running devbox shell in environment with exported Bash function

How was it tested?

Tested that when running the below commands:

• no errors are printed
• the foo function runs successfully and prints foo

Case 1 (simple):

foo() { echo foo; }
export -f foo
devbox shell
foo

Case 2 (function that contains special characters " and $):

foo() { echo "${bar}"; }
export -f foo
export bar=foo
devbox shell
foo

Case 3 (shellenv):

foo() { echo foo; }
export -f foo
devbox shellenv > shellrc

# open a new shell

source shellrc
foo

Also added a Bash function to the test data used by TestWriteDevboxShellrc.

Community Contribution License

All community contributions in this pull request are licensed to the project
maintainers under the terms of the
Apache 2 License.

By creating this pull request, I represent that I have the right to license the
contributions to the project maintainers under the Apache 2 License as stated in
the
Community Contribution License.

[savil]

Thank you for sending this!

I struggled to repro the bug on my mac, but could using a fedora docker container. Confirmed that using the binary from this PR fixes the issue as well.