Automatically update SPM version variable (#7593)

Author: paulb777

ReleaseTooling/Sources/FirebaseReleaser/InitializeRelease.swift

@@ -25,6 +25,7 @@ struct InitializeRelease {
     let branch = createReleaseBranch(path: gitRoot, version: manifest.version)
     updatePodspecs(path: gitRoot, manifest: manifest)
     updatePodfiles(path: gitRoot, version: manifest.version)
+    updateSwiftPackageVersion(path: gitRoot, version: manifest.version)
     return branch
   }
 
@@ -128,4 +129,10 @@ struct InitializeRelease {
       "'Firebase',[[:space:]]*'\\).*'#\\1\(version)'#\" Podfile"
     Shell.executeCommand(sedCommand2, workingDir: collisionPodfile)
   }
+
+  private static func updateSwiftPackageVersion(path: URL, version: String) {
+    // Match strings like `let firebaseVersion = "7.7.0"` and update the version.
+    Shell.executeCommand("sed -i.bak -e \"s/\\(let firebaseVersion.*=[[:space:]]*\\).*/\\1" +
+      "\\\"\(version)\\\"/\" Package.swift", workingDir: path)
+  }
 }