[osgearth] Fix errors that occur in the osgearth config file on some platforms

[cbrl]

Describe the pull request

• What does your PR fix?

  Fixes the exported target in osgEarthConfig.cmake. Though it seems to work on Windows, on other platforms (e.g. Linux) the capitalization of the find_path argument causes the operation to fail, and the lack of the library definition causes an error upon attempting to set that target's properties.

• Which triplets are supported/not supported? Have you updated the CI baseline?

  Unchanged

• Does your PR follow the maintainer guide?

  Yes

• If you have added/updated a port: Have you run ./vcpkg x-add-version --all and committed the result?

  Yes

[ghost]

All CLA requirements met.

[Cheney-W]

Local testing in progress.

[ras0219-msft]

Thanks for the PR! LGTM with the one suggestion applied.

[Cheney-W]

versions/o-/osgearth.json#L2
versions/o-/osgearth.json(2,): error : While reading versions for port osgearth from file: version/o-/osgearth.json
File declares version 3.3#1 with SHA: 1198ef439cf8f6851e6b3accbe668c34a46c8ba6
But local port with the same version has a different SHA: 1091743df235c6472d30b157723f82e6d3473cc9
Please update the port's version fields and then run:

vcpkg x-add-version osgearth
git add versions
git commit -m "Update version database"

to add a new version.

[Cheney-W]

Please don't change port-version twice in one PR, you need to change the value of port-version back to 1, and then execute the following command:

1. <modify file>
2. git add .
3. git commit -m "xxx"
4. .\vcpkg.exe x-add-version osgearth --overwrite-version
5. git add .
6. git commit --amend --no-edit
7. git push

[cbrl]

Sorry about that. I amended the modification with the proper port version.

Suggestion was applied

[BillyONeal]

Thanks!