Rename nightly_6_1 params to nightly_next (#65)

Rename nightly_6_1 params to nightly_next; see
apple/swift-nio#3122

Author: rnro

.github/workflows/main.yml

@@ -18,5 +18,5 @@ jobs:
       linux_5_10_arguments_override: "-Xswiftc -warnings-as-errors --explicit-target-dependency-import-check error"
       # TODO: Enable warnings-as-errors on 6.0.
       linux_6_0_arguments_override: "-Xswiftc -strict-concurrency=complete --explicit-target-dependency-import-check error"
-      linux_nightly_6_1_arguments_override: "-Xswiftc -strict-concurrency=complete --explicit-target-dependency-import-check error"
+      linux_nightly_next_arguments_override: "-Xswiftc -strict-concurrency=complete --explicit-target-dependency-import-check error"
       linux_nightly_main_arguments_override: "-Xswiftc -strict-concurrency=complete --explicit-target-dependency-import-check error"

.github/workflows/pull_request.yml

@@ -22,7 +22,7 @@ jobs:
       linux_5_10_arguments_override: "-Xswiftc -warnings-as-errors --explicit-target-dependency-import-check error"
       # TODO: Enable warnings-as-errors on 6.0.
       linux_6_0_arguments_override: "-Xswiftc -strict-concurrency=complete --explicit-target-dependency-import-check error"
-      linux_nightly_6_1_arguments_override: "-Xswiftc -strict-concurrency=complete --explicit-target-dependency-import-check error"
+      linux_nightly_next_arguments_override: "-Xswiftc -strict-concurrency=complete --explicit-target-dependency-import-check error"
       linux_nightly_main_arguments_override: "-Xswiftc -strict-concurrency=complete --explicit-target-dependency-import-check error"
 
   cxx-interop: