chore: Use GPL license with https.

[iphydf]

This aligns with the new zig-toxcore-c repo. It is a chore, but better than changing the zig-toxcore-c license to not use https.

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This change is 

[nurupo]

I have diffed the license with https://www.gnu.org/licenses/gpl-3.0.txt and they exactly match.

Cirrus builds fails with:

(02:09:21) ERROR: /src/workspace/c-toxcore/BUILD.bazel:4:8: no such target '//tools:LICENSE.gpl3-https': target 'LICENSE.gpl3-https' not declared in package 'tools' defined by /src/workspace/tools/BUILD.bazel (Tip: use `query "//tools:*"` to see all the targets in that package) and referenced by '//c-toxcore:license_test'

Fix this and it should be good to go.

Reviewed 2 of 2 files at r1, all commit messages.
Reviewable status: complete! 1 of 1 approvals obtained

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (0e42752) 69.01% compared to head (ebafd51) 69.03%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2515      +/-   ##
==========================================
+ Coverage   69.01%   69.03%   +0.02%     
==========================================
  Files          89       89              
  Lines       27781    27781              
==========================================
+ Hits        19174    19180       +6     
+ Misses       8607     8601       -6     

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