Update testnet flag when upgrading testnets

[jcortejoso]

Description

yarn upgrade:<testnet> is not setting testnet flag for some of the public EVMS:

╰─ yarn upgrade:mumbai
yarn run v1.22.19
$ export NETWORK=mumbai&&yarn run upgrade --network mumbai
$ npx hardhat run ./scripts/deploy/truffle-wrapper/upgradeContractsWrapper.js --network mumbai
testnet false

Is this PR related with an open issue?

Related to Issue #

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• Follows the code style of this project.
• Tests Cover Changes
• Documentation

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