Removed old-style-cast from Plumed.h #2954

Job	Run time
codecheck / codecheck	43m 18s
docker / docker (fedora39)	20m 52s
linux / linux (-doc-mpi-)	38m 23s
docker / docker (rocky8)	23m 34s
linux / linux (-mpi-)	50m 57s
linux / linux (-coverage-mpi-)	1h 0m 8s
conda / conda (ubuntu-20.04)	10m 25s
conda / conda (macos-12)	19s
linux / linux (-debug-)	30m 35s
mac / macports (macos-12)	18m 5s
mac / macsimple (macos-12)	11m 1s
linux / linux (-debug-mpi-)	39m 47s
conda / conda (macos-14)	12s
mac / macsimple (macos-14)	4m 28s
mac / macports (macos-14)	8m 27s
linux / linux (-intel-)	44m 13s
mac / macports (+allmodules, macos-12)	23m 12s
linux / linux (-pycv-mpi-)	17m 0s
	7h 24m 56s

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