ci: skip crates.io dep run when releasing (#995)

#993 introduces changes in a sub crate that other Tokio crates depend
on. To make CI pass, a `[patch]` statement and `path` dependencies are
used.

When releasing, these must be removed. However, the commit that
removes them and prepares the crates for release will not be able to
pass CI.

This commit adds a conditional on a special `[ci-release]` snippet in
the commit message. If this exists, CI is only run with the full "patched"
dependencies.

.cirrus.yml

@@ -15,6 +15,18 @@ task:
     - sh rustup.sh -y
     - . $HOME/.cargo/env
     - rustup target add i686-unknown-freebsd
+    - |
+      # Remove any existing patch statements
+      mv Cargo.toml Cargo.toml.bck
+      sed -n '/\[patch.crates-io\]/q;p' Cargo.toml.bck > Cargo.toml
+
+      # Patch all crates
+      cat ci/patch.toml >> Cargo.toml
+
+      # Print `Cargo.toml` for debugging
+      echo "~~~~ Cargo.toml ~~~~"
+      cat Cargo.toml
+      echo "~~~~~~~~~~~~~~~~~~~~"
   cargo_cache:
     folder: $HOME/.cargo/registry
   test_script:
@@ -23,6 +35,7 @@ task:
     - cargo doc --all
   i686_test_script:
     - . $HOME/.cargo/env
-    - cargo test --all --exclude tokio-tls --no-fail-fast --target i686-unknown-freebsd
+    - |
+      cargo test --all --exclude tokio-tls --no-fail-fast --target i686-unknown-freebsd
   before_cache_script:
     - rm -rf $HOME/.cargo/registry/index