[ImgBot] Optimize images

*Total -- 2,243.88kb -> 1,561.66kb (30.4%)

/src/doc/rustc-dev-guide/src/img/wpa-stack.png -- 142.16kb -> 74.95kb (47.28%)
/src/doc/rustc-dev-guide/src/img/coverage-branch-counting-01.png -- 11.02kb -> 6.11kb (44.58%)
/src/doc/rustc/src/images/llvm-cov-show-01.png -- 406.98kb -> 242.59kb (40.39%)
/src/doc/rustc-dev-guide/src/img/llvm-cov-show-01.png -- 406.98kb -> 242.59kb (40.39%)
/src/doc/rustc-dev-guide/src/queries/example-0.png -- 104.08kb -> 65.67kb (36.9%)
/src/doc/rustc-dev-guide/src/img/github-cli.png -- 26.16kb -> 17.17kb (34.36%)
/src/doc/rustc-dev-guide/src/img/submodule-conflicts.png -- 19.74kb -> 13.10kb (33.63%)
/src/doc/rustc-dev-guide/src/img/dataflow-graphviz-example.png -- 79.97kb -> 53.10kb (33.6%)
/src/doc/rustc-dev-guide/src/img/rustbot-submodules.png -- 25.42kb -> 17.63kb (30.64%)
/src/doc/rustdoc/src/images/collapsed-long-item.png -- 16.62kb -> 12.24kb (26.37%)
/src/doc/rustc-dev-guide/src/img/other-peoples-commits.png -- 294.45kb -> 216.95kb (26.32%)
/src/doc/rustc-dev-guide/src/img/github-whitespace-changes.png -- 28.53kb -> 21.22kb (25.64%)
/src/doc/rustdoc/src/images/collapsed-trait-impls.png -- 43.19kb -> 32.20kb (25.45%)
/src/doc/rustc/src/images/image1.png -- 161.03kb -> 129.72kb (19.45%)
/src/doc/rustc/src/images/image2.png -- 151.67kb -> 123.64kb (18.48%)
/src/doc/rustc-dev-guide/src/img/wpa-initial-memory.png -- 305.31kb -> 272.61kb (10.71%)
/src/librustdoc/html/static/images/favicon-32x32.png -- 1.10kb -> 1.04kb (4.89%)
/src/doc/rustc/src/images/image3.png -- 19.47kb -> 19.11kb (1.83%)

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