use 1.90 for semver_checks and pin semver_checks to 0.43.0 (#793)

In order to not bump MSRV we have to do a kind of weird
juggling with version numbers.

Author: molpopgen

.github/workflows/semver.yml

@@ -23,5 +23,9 @@ jobs:
         uses: baptiste0928/[email protected]
         with:
           crate: cargo-semver-checks
+          version: '0.43.0'
       - name: run check-release
-        run: cargo semver-checks check-release
+      # We set the cargo version here to dodge ecosystem
+      # issues that can arise b/c semver-checks doesnt'
+      # respect our Cargo.lock
+        run: cargo +1.90.0 semver-checks check-release