…er#345)

Bumps [github.com/coder/serpent](https://github.com/coder/serpent) from
0.14.0 to 0.15.0.
<details>
<summary>Commits</summary>
<ul>
<li><a
href="https://github.com/coder/serpent/commit/40b60bf4c1495caddc0292f862de275da292e6aa"><code>40b60bf</code></a>
Merge pull request <a
href="https://redirect.github.com/coder/serpent/issues/32">#32</a> from
coder/fix/allow-empty-env-values</li>
<li><a
href="https://github.com/coder/serpent/commit/e9b06829ec563f79b757fd4e82ddf558b7075a4c"><code>e9b0682</code></a>
test: add ValueSource assertions and unset env var test</li>
<li><a
href="https://github.com/coder/serpent/commit/00997cc0479fb5e65d4c58ef785c54e9ae95e59c"><code>00997cc</code></a>
fix: allow empty environment variable values to override defaults</li>
<li>See full diff in <a
href="https://github.com/coder/serpent/compare/v0.14.0...v0.15.0">compare
view</a></li>
</ul>
</details>
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Co-authored-by: Ethan Dickson <ethan@coder.com>