Fix build of listmonk executable on arm64 and armhf

[ruairif]

Problem

Installing listmonk on ARM systems results in an error #30

Solution

By changing in to the directory containing the listmonk source before attempting to build the executable when running on ARM based systems.

PR Status

• [x] Code finished and ready to be reviewed/tested
• [x] The fix/enhancement were manually tested (if applicable)

Automatic tests

Automatic tests can be triggered on https://ci-apps-dev.yunohost.org/ after creating the PR, by commenting "!testme", "!gogogadgetoci" or "By the power of systemd, I invoke The Great App CI to test this Pull Request!". (N.B. : for this to work you need to be a member of the Yunohost-Apps organization)

[navanchauhan]

!testme

[yunohost-bot]

Fingers crossed!