changing push trigger to be just for main

[jiyoontbd]

Changed ci.yml so that push triggers only on pushes to main.

[codecov[bot]]

Codecov Report

Merging #247 (ef28c31) into main (1486951) will not change coverage. The diff coverage is n/a.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #247 +/- ## ======================================= Coverage 80.04% 80.04% ======================================= Files 37 37 Lines 2200 2200 Branches 312 312 ======================================= Hits 1761 1761 Misses 299 299 Partials 140 140 ``` | [Components](https://app.codecov.io/gh/TBD54566975/web5-kt/pull/247/components?src=pr&el=components&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=TBD54566975) | Coverage Δ | | |---|---|---| | [credentials](https://app.codecov.io/gh/TBD54566975/web5-kt/pull/247/components?src=pr&el=component&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=TBD54566975) | `82.06% <ø> (ø)` | | | [crypto](https://app.codecov.io/gh/TBD54566975/web5-kt/pull/247/components?src=pr&el=component&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=TBD54566975) | `45.07% <ø> (ø)` | | | [dids](https://app.codecov.io/gh/TBD54566975/web5-kt/pull/247/components?src=pr&el=component&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=TBD54566975) | `89.71% <ø> (ø)` | | | [common](https://app.codecov.io/gh/TBD54566975/web5-kt/pull/247/components?src=pr&el=component&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=TBD54566975) | `69.44% <ø> (ø)` | |

[jiyoontbd]

cc @leordev