ci: set E2E_SHARD_TOTAL as env variable

[alan-agius4]

Whlist this defaults to 1 when not supplied, it's cleaner that this is 1. Also, this is not an action input.

[alan-agius4]

This PR was merged into the repository. The changes were merged into the following branches:

• main: 290ac55
• 20.2.x: f942424

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