gnu: shells.scm: Prefix license identifiers.

gnu: shells.scm: Prefix license identifiers.

* gnu/packages/shells.scm (dash):
(fish):
(fish-foreign-env):
(rc):
(es):
(tcsh):
(zsh):
(xonsh):
(scsh):
(linenoise):
(s-shell):
(oksh):
(loksh):
(mksh):
(oil):
(gash):
(gash-utils):
(rust-nu-cli-0.26):
(rust-nu-command-0.26):
(rust-nu-data-0.26):
(rust-nu-engine-0.26):
(rust-nu-errors-0.26):
(rust-nu-json-0.26):
(rust-nu-parser-0.26):
(rust-nu-plugin-0.26):
(rust-nu-plugin-binaryview-0.26):
(rust-nu-plugin-chart-0.26):
(rust-nu-plugin-fetch-0.26):
(rust-nu-plugin-from-bson-0.26):
(rust-nu-plugin-from-sqlite-0.26):
(rust-nu-plugin-inc-0.26):
(rust-nu-plugin-match-0.26):
(rust-nu-plugin-post-0.26):
(rust-nu-plugin-ps-0.26):
(rust-nu-plugin-s3-0.26):
(rust-nu-plugin-selector-0.26):
(rust-nu-plugin-start-0.26):
(rust-nu-plugin-sys-0.26):
(rust-nu-plugin-textview-0.26):
(rust-nu-plugin-to-bson-0.26):
(rust-nu-plugin-to-sqlite-0.26):
(rust-nu-plugin-tree-0.26):
(rust-nu-plugin-xpath-0.26):
(rust-nu-protocol-0.26):
(rust-nu-source-0.26):
(rust-nu-stream-0.26):
(rust-nu-table-0.26):
(rust-nu-test-support-0.26):
(rust-nu-value-ext-0.26): Prefix license identifier.