Update Firebase SPM version to 7.6.0

[4brunu]

Firebase was updated to version 7.6.0 but the SPM version was still on 7.5.0, so I opened this PR to fix it.

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[4brunu]

@googlebot I signed it!

[paulb777]

Thanks!

[4brunu]

Could you please create a new tag to reference in SPM? Thanks

[paulb777]

Note that the 7.6.0 release was still getting installed. The fix only impacts the version logged with the release.

I'll need to wait for #7533 to get this change approved to the release branch to update the tag. Since today is a holiday, this may not happen until tomorrow.

[4brunu]

Thanks 👍

[paulb777]

The tag is now updated. Thanks @4brunu!

[4brunu]

Thanks for your help and the quick resolution of this 👍