Merge branch 'main' into release/v2

* main:
  Prepare for release 2.11.1.
  Update npm packages.
  Bump @actions/core from 1.2.4 to 1.2.6
  Update to gradle 6.7-rc-1 for test fixture. Build with Java 15 on CI.
  Improve GitHub Actions Gradle cache.
  Add square/radiography to adopter list
  Add cashapp/copper to adapter list
  SDK Build tools 30.0.2.
  Update fixture dependencies.
  Gradle 6.6.
  Update README.md
  Update packages.
  Build tools 30.0.1.
  Use fs for writing licence files.
  Update cmdline-tools to 2.1.

node_modules/@actions/tool-cache/lib/retry-helper.d.ts

@@ -0,0 +1,12 @@
+/**
+ * Internal class for retries
+ */
+export declare class RetryHelper {
+    private maxAttempts;
+    private minSeconds;
+    private maxSeconds;
+    constructor(maxAttempts: number, minSeconds: number, maxSeconds: number);
+    execute<T>(action: () => Promise<T>, isRetryable?: (e: Error) => boolean): Promise<T>;
+    private getSleepAmount;
+    private sleep;
+}