[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.

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Apache 2 License.

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contributions to the project maintainers under the Apache 2 License as stated in
the
Community Contribution License.