Enable Swift 6.1 jobs in CI (#59)

Motivation:

Swift 6.1 has been released, we should add it to our CI coverage.

Modifications:

Add additional Swift 6.1 jobs where appropriate in main.yml,
pull_request.yml

Result:

Improved test coverage.

.github/workflows/main.yml

@@ -14,6 +14,7 @@ jobs:
       linux_5_9_enabled: false
       linux_5_10_enabled: false
       linux_6_0_arguments_override: "--explicit-target-dependency-import-check error -Xswiftc -require-explicit-sendable"
+      linux_6_1_arguments_override: "--explicit-target-dependency-import-check error -Xswiftc -require-explicit-sendable"
       linux_nightly_next_arguments_override: "--explicit-target-dependency-import-check error -Xswiftc -require-explicit-sendable"
       linux_nightly_main_arguments_override: "--explicit-target-dependency-import-check error -Xswiftc -require-explicit-sendable"
 

.github/workflows/pull_request.yml

@@ -23,6 +23,7 @@ jobs:
       linux_5_9_enabled: false
       linux_5_10_enabled: false
       linux_6_0_arguments_override: "--explicit-target-dependency-import-check error -Xswiftc -require-explicit-sendable"
+      linux_6_1_arguments_override: "--explicit-target-dependency-import-check error -Xswiftc -require-explicit-sendable"
       linux_nightly_next_arguments_override: "--explicit-target-dependency-import-check error -Xswiftc -require-explicit-sendable"
       linux_nightly_main_arguments_override: "--explicit-target-dependency-import-check error -Xswiftc -require-explicit-sendable"