Bump MSRV to 1.63 since gexiv2-sys/glib-sys will require it

[felixc]

Unblocks #62

[codecov[bot]]

Codecov Report

Base: 68.96% // Head: 68.96% // No change to project coverage :thumbsup:

Coverage data is based on head (41774f4) compared to base (24e9cdd). Patch coverage: 0.00% of modified lines in pull request are covered.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #63 +/- ## ======================================= Coverage 68.96% 68.96% ======================================= Files 1 1 Lines 928 928 ======================================= Hits 640 640 Misses 288 288 ``` | [Impacted Files](https://codecov.io/gh/felixc/rexiv2/pull/63?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Felix+Crux) | Coverage Δ | | |---|---|---| | [src/lib.rs](https://codecov.io/gh/felixc/rexiv2/pull/63?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Felix+Crux#diff-c3JjL2xpYi5ycw==) | `68.96% <0.00%> (ø)` | | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Felix+Crux). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Felix+Crux)

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