CI: Create branch release/0.22. Update CI & Clippy config for it.

Jobs just silently wait forever since they are waiting for an 18.04
runner and there are none anymore. Fix that.

Ubuntu 22.04 doesn't have clang-10. Fix that by syncing mk/* with
the versions in the *ring* main branch.

To minimize changes to the source code, turn off newer Clippy lints.

.github/workflows/ci.yml

@@ -7,7 +7,7 @@ jobs:
     # Don't run duplicate `push` jobs for the repo owner's PRs.
     if: github.event_name == 'push' || github.event.pull_request.head.repo.full_name != github.repository
 
-    runs-on: ubuntu-18.04
+    runs-on: ubuntu-22.04
 
     steps:
       - uses: actions-rs/toolchain@v1
@@ -22,7 +22,7 @@ jobs:
     # Don't run duplicate `push` jobs for the repo owner's PRs.
     if: github.event_name == 'push' || github.event.pull_request.head.repo.full_name != github.repository
 
-    runs-on: ubuntu-18.04
+    runs-on: ubuntu-22.04
 
     steps:
       - uses: actions-rs/toolchain@v1
@@ -39,7 +39,7 @@ jobs:
     # Don't run duplicate `push` jobs for the repo owner's PRs.
     if: github.event_name == 'push' || github.event.pull_request.head.repo.full_name != github.repository
 
-    runs-on: ubuntu-18.04
+    runs-on: ubuntu-22.04
 
     steps:
       - uses: actions-rs/toolchain@v1
@@ -67,7 +67,7 @@ jobs:
     # Don't run duplicate `push` jobs for the repo owner's PRs.
     if: github.event_name == 'push' || github.event.pull_request.head.repo.full_name != github.repository
 
-    runs-on: ubuntu-18.04
+    runs-on: ubuntu-22.04
 
     steps:
       - uses: actions-rs/toolchain@v1
@@ -94,7 +94,7 @@ jobs:
     # Don't run duplicate `push` jobs for the repo owner's PRs.
     if: github.event_name == 'push' || github.event.pull_request.head.repo.full_name != github.repository
 
-    runs-on: ubuntu-18.04
+    runs-on: ubuntu-22.04
 
     strategy:
       matrix:
@@ -162,16 +162,16 @@ jobs:
 
         include:
           - target: arm-unknown-linux-gnueabihf
-            host_os: ubuntu-18.04
+            host_os: ubuntu-22.04
 
           - target: i686-pc-windows-msvc
             host_os: windows-latest
 
           - target: x86_64-unknown-linux-musl
-            host_os: ubuntu-18.04
+            host_os: ubuntu-22.04
 
           - target: x86_64-unknown-linux-gnu
-            host_os: ubuntu-18.04
+            host_os: ubuntu-22.04
 
     steps:
       - if: ${{ contains(matrix.host_os, 'ubuntu') }}
@@ -224,7 +224,7 @@ jobs:
         # TODO: targets
         include:
           - target: x86_64-unknown-linux-musl
-            host_os: ubuntu-18.04
+            host_os: ubuntu-22.04
 
     steps:
       - if: ${{ contains(matrix.host_os, 'ubuntu') }}