fix(core): do not override process.env with variables in dotenv files

[leosvelperez]

Current Behavior

Variables in dotenv files are overriding process.env variables.

Expected Behavior

Variables in dotenv files should not override process.env variables.

Related Issue(s)

Fixes #6523

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Nx Cloud Report

CI ran the following commands for commit 09f6f74. Click to see the status, the terminal output, and the build insights.

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Status	Command
	nx affected --target=build --base=117ee9308a4e4aabb5bf5aa4023cce5fd23feac3 --parallel --max-parallel=3
	nx affected --target=e2e --base=117ee9308a4e4aabb5bf5aa4023cce5fd23feac3
	nx affected --target=lint --base=117ee9308a4e4aabb5bf5aa4023cce5fd23feac3 --parallel --max-parallel=4
	nx affected --target=test --base=117ee9308a4e4aabb5bf5aa4023cce5fd23feac3 --parallel --max-parallel=2
	nx build typedoc-theme

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