In PR #26786, the Go version for golangci-lint is bumped to 1.21. This
causes the following error:
```
models/migrations/v1_16/v210.go:132:23: SA1019: elliptic.Marshal has been deprecated since Go 1.21: for ECDH, use the crypto/ecdh package. This function returns an encoding equivalent to that of PublicKey.Bytes in crypto/ecdh. (staticcheck)
PublicKey: elliptic.Marshal(elliptic.P256(), parsed.PubKey.X, parsed.PubKey.Y),
```
The change now uses [func (*PublicKey)
ECDH](https://pkg.go.dev/crypto/ecdsa#PublicKey.ECDH), which is added in
Go 1.20.
The xorm `Sync2` has already been deprecated in favor of `Sync`,
so let's do the same inside the Gitea codebase.
Command used to replace everything:
```sh
for i in $(ag Sync2 --files-with-matches); do vim $i -c ':%sno/Sync2/Sync/g' -c ':wq'; done
```
Replace #23350.
Refactor `setting.Database.UseMySQL` to
`setting.Database.Type.IsMySQL()`.
To avoid mismatching between `Type` and `UseXXX`.
This refactor can fix the bug mentioned in #23350, so it should be
backported.
Change all license headers to comply with REUSE specification.
Fix #16132
Co-authored-by: flynnnnnnnnnn <flynnnnnnnnnn@github>
Co-authored-by: John Olheiser <john.olheiser@gmail.com>
