Bump Kani version to 0.26.0

* The Kani reference now includes an
  ["Attributes"](https://model-checking.github.io/kani/reference/attributes.html)
  section that describes each of the attributes available in Kani (by
  @adpaco-aws)
* Users' choice of SAT solver, specified by the `solver` attribute, is
  now propagated to the loop-contract synthesizer (by @qinheping)
* Unit tests generated by the concrete playback feature now compile
  correctly when using `RUSTFLAGS="--cfg=kani"` (by @jaisnan)
* The Rust toolchain is updated to 2023-02-16 (by @tautschnig)

Author: karkhaz

CHANGELOG.md

@@ -8,10 +8,10 @@ This file was introduced starting Kani 0.23.0, so it only contains changes from
 
 ### What's Changed
 
-* The Kani reference now includes an ["Attributes"](https://model-checking.github.io/kani/reference/attributes.html) section that describes each of the attributes available in Kani (by @adpaco-aws)
-* Users' choice of SAT solver, specified by the `solver` attribute, is now propagated to the loop-contract synthesizer (by @qinheping)
-* Unit tests generated by the concrete playback feature now compile correctly when using `RUSTFLAGS="--cfg=kani"` (by @jaisnan)
-* The Rust toolchain is updated to 2023-02-16 (by @tautschnig)
+* The Kani reference now includes an ["Attributes"](https://model-checking.github.io/kani/reference/attributes.html) section that describes each of the attributes available in Kani ([pull request](https://github.com/model-checking/kani/pull/2359) by @adpaco-aws)
+* Users' choice of SAT solver, specified by the `solver` attribute, is now propagated to the loop-contract synthesizer ([pull request](https://github.com/model-checking/kani/pull/2320) by @qinheping)
+* Unit tests generated by the concrete playback feature now compile correctly when using `RUSTFLAGS="--cfg=kani"` ([pull request](https://github.com/model-checking/kani/pull/2353) by @jaisnan)
+* The Rust toolchain is updated to 2023-02-18 ([pull request](https://github.com/model-checking/kani/pull/2384) by @tautschnig)
 
 **Full Changelog**: https://github.com/model-checking/kani/compare/kani-0.25.0...kani-0.26.0